Somebody moved all the stuff off the shelf.

Delusion, interference, something like that.

Ghost.  btw, why did it want them out of the house?  Did it catch on fire or something or was the voice just being antisocial?

The spring inside of the toy carrousel was getting weak and could only barely and occasional move the internal mechanisms

The front tire blew out which caused the steering wheel to jerk in the direction of the side that the tire blew.  That's pretty obvious.

If none of these answers are satisfactory then Jake did it.

A powered toy carrousel?  Have you ever seen one?  They are wind up.  sheesh

I'm sorry, I was referring to nuclear powered carrousels.

Oh, CARROUSELS. I thought we were talking about submarines.

Hi Knight!

I'd be glad to help.

Are you suggesting this was some sort of spiritual event?  Believe it or not, most incidents like this tend to be caused by a family member who just either (1) forgot they'd cleared it or (2) was never asked if they did.  This sounds like either your dad, or siblings, cleared off the shelf (perhaps even over time and you just realized it at that moment when you decided you needed a place for the printer).

Children hear all sorts of things, and you're no different.  It could have been your mom or dad saying that from another room.  You should not let tricks of the mind tease you into believing that these seemingly-paranoid thoughts represent an actual being. 

Stress.  Often times people "experience" so-called supernatural events when they are at their most tense or when they are stressed out about something.  Often times it reflects personal emotions.  Perhaps they needed a night out?  Also be wary about incidents like this.  Often times, societal pressure or peer pressure is involved.  It's called memory contamination.  It goes something like this...

"Hunny did you hear that?"

"What?"

"It sounded like something."

"A male voice?"

"Maybe...yeah."

Etc...

When your brain does not fully analyze an event, or can't for whatever reason, it fills in blanks.  It is like the "Phoenix lights" where people thought they were seeing an alien spacecraft, but really they were seeing flares from Air Force craft flying over the area.  The flares fell in a pattern, and because it was dark, people filled in the blank space behind the flares with blackness, making it appear as if the flares were lights circling a very large spacecraft. 

A similar event that you may interpret easier is when in the middle of the night, you may reach over and try to grab something off a night stand or walk to the bathroom.  Your senses will play tricks on you, and you may miss the nightstand by a few inches or more because your eyes did not interpret the distance correctly...or you may walk into a wall for the same reasons. 

Um, does it have a "wind-up" aperture?  Often times those things get stuck, and sometimes they unwind, and go for a few seconds, sometimes longer.  Ever wind up a toy, put it on the ground, and have it walk a few feet then stop...and you'd have to pick it up (holding the feet) and move it, set it back down and it would go again?  Same sort of thing. 

I think she's been listening to "Jesus Take the Wheel" a little too much for her own good.  The steering column is connected to the tires.  If the tires are following the road, often times it will follow the grooves of the road made from previous cars which drive over these roads all the time.  These are really weak arguments, and many have logical or natural explanations.  It seems like your mom just wants to believe the supernatural explanations because she has been raised to believe them all her life.

I suggest you take the time to read my article on ghost stories and hauntings and how they evolve over time. 

Well, then what will she buy? These arguments are all extraordinarily weak, the sorts of phenomenon that are easily explained with some simple investigation. There is no reason to invent an entirely seperate ontological reality that can unknowingly interact with the material world on the basis of words heard whispered on CDs and the motion of cars due the flat tyres. There is no logical connection between the assertion (a) that there exists a realm wholly seperate for and responsible for maintaining the physical universe on the basis of some conscious entity which exercises control over the world we experience and (b) the 5 arguments just put forth. The precise refutations of each point have already been given, but it sounds like what is really needed is just some basic understanding of logic and epistemology. There first thing to note is that she is making an ad ignorantium fallacy, effectively assuming her explanation to be a sort of "default" until a proper explanation can be brought in. Yet, as we have seen, there is no meaningful justificatory grounds to assume this "default" especially when it is so extravagant as to reinvent the ontological basis for reality. Second, she is demanding we give a precise explanation for a phenomenon whilst simultaneously exempting herself from doing the same. Just for kicks, ask her to outline the proposed mechanism in a very clear way as to the manner in which some supernatural event was responsible for these phenomenon. If she responds with just those words, start asking technical questions such as "how does this supernatural entity have causal powers given that you've exempted physical causality from its properties?", etc. These questions will demonstrate her "default" explanation collapses for reasons of both logic and ontology.

My immediate impression is that your mother needs to be better versed in lateral thinking. Lateral thinking is, as the name suggests, broad in scope. It comes in most useful when everyday problems have apparantly no solution. The solution might be so obvious that it is hidden in plain sight, but because we tend to miss these, we invent overly complex explanations for phenomenon. Revising the ontological basis of reality on the basis of such experiences is one example. An exercise in this type of thinking should teach us that the "first thing that comes to mind" when we try to envisage a solution to an otherwise unexplained phenomenon is very rarely trustworty. These sorts of situations are commonplace. A few weeks ago, when I logged into my laptop, it simply entered the account without a password, as normally needed. The first thought that came to my mind was "someone's hacked it". But, knowing about lateral thinking and parsimony, I realized that was ridiculous, so I checked the control panel settings and realized the computer had opened the account on its own because I had recently set it to standby after a few minutes so it wouldn't lose battery power. This sort of thing happens all the time. We lose clothes and immediately think of theives and pranksters, but it turns out to be our own carelessness. Don't trust the default explanation, it is riddled with psychological bias.

I doubt that if more than 1 person heard the same thing it was imaginary, but there are other explanations:

Coincidence: "Put your toy down" was part of the song or there was deliberate or accidental interference, "Get out of the house" was said be a neighbor fighting with a spouse, or someone said it at the window as a joke, etc.

There's also (I forget the term) the phenonmena where any noise can sound like a voice (this is why there are words heard when records are played backwards - assuming it wasn't purposely added - also the reason for "EVP"'s Especially if one heard it and said to the other what they thought they heard.

A couple of my friends once played a joke on an old woman who claimed to be a with by getting a universal remote and changing the channels on her TV from the window. They said she bowed down and worshipped the "spirit."

*** Edit to add that I just want to point out that giving a supernatural explanation just because you don't know exactly why something happened is very poor reasoning.

Need more info.  Were there things on other shelves above and below the shelf that was cleared, and if so, did they move at all?  Was anyone watching the shelf at the time?  Could you tell the direction of initial motion for the objects?  Was it horizontal or was there an initial vertical component?  Did the objects tumble or did they slide?  Did you notice anything else unusual at the time, such as a minor earthquake or a car driving by with a loud stereo?  Was anyone in the room thinking or talking about that specific shelf at the time?  Have you used a level to determine if the shelf was truly flat?  What kinds of objects were on the shelf?

Hmm... if no one was watching the shelf at the time, then I would expect that to mean that the observations are less reliable... if the shelf wasn't being directly observed, then the brain has less input on the event, and that would leave more room for it to "fill in the blanks" with imagination and false memory.  Since it happened a long time ago, that makes the remembered details even more suspect.  Still, if you remember witnessing it and your parents also remember witnessing it, that pretty well rules out a dream as a possible explanation.  If you're correct that the objects on the other shelves didn't in fact move at all, that would seem to rule out any shaking of the bookshelf.  Still, things don't just happen without a cause.  Assuming everything happened the way you describe it, and assuming the objects weren't somehow rigged as a joke, I don't see any physical explanation, but even if the cause is spiritual in nature, there's no reason to attribute it to a god.  Why would a god care about where someone puts their printer?  If the cause is spiritual in nature, I would think it more likely that it was either you, one of your parents, or perhaps something akin to a ghost.  Nikolaj nailed this one pretty well, I think:

The only thing I would add is that if you're really curious, you can still investigate... just be careful not to jump to any conclusions.

From a psychological point of view this could simply be a case of suggestion.  No way to tell where it started but the mind is able to conjure up some pretty bizarre stuff.  The power of suggestion can cause all sorts of illusions, including hallucinations in extreme cases.  There have been some excellent explanations here and they are probably quite accurate in as much as the shelf might have been cleared by someone else in the house who thought the response was a good practical joke, or your mom's memory of cleaning the shelf is vague; at the time she was cleaning she could have been thinking about something impacting your lives, or simply something important to her in a personal vein.  The emotions or thoughts involved in this could have easily blurred her memory.

Often we can be thinking of something (an incident, a movie recently watched or just about anything) which triggers a past memory or subconscious thought and we think we hear something, a noise or voice and sometimes this even manifests itself as a recognizable phrase. In any event these are in no way of divine origin.  If all of us here are wrong (highly doubtful) and there is a god, then he's a practical joker and not someone I would trust with my immortal soul.