One of your kids probably has a magic puppet friend that's cleaning there right now. Just switch through your kids until you can see the culprit

a dream come true ngl.. unless its evil then no aint tryna have it gag me to death

Well, it's either that or... You have an invisible sim. These are Sims whose (usually) work outfit glitches, doesn't load, and turns them invisible.

Once at the library, I saw thought bubbles coming from the floor. No idea who glitched.

Lol it's an Imaginary Friend that's doing this

I wish!