When I was 15ish, I had this nightly routine. I stayed up later than my whole family, and before I would go to bed it was my responsiblity to wake my little sisters up and make them use the bathroom. This may seem weird, but they all grew so fast that their bladders had a hard time keeping up. At that time my little sisters were 3, 4, 4, 5, and 8 years old. (Yes there is 1 set of twins)
It was a pretty normal thing, until they started having blocks in their underwear.
Every night for a week, when I would go to do this, I would find some small toy or building block in their pajamas. I was completely confused.
I asked them about it during the day and they all had no idea what I was talking about.
Then one day, my mother starts to fall asleep while my one of the twins is in the room. My sister leans over my mother to make sure she is asleep, creeps out of the room, comes back in and goes to put a block in my moms pants. My mother, who had not been fully asleep, asked her why. Her response was that she wanted her to have a toy to sleep with.
We informed her that it wasn't polite to go sticking things down people's pants, which is a valuable life lesson.
The moral of this story is kids are weird and there is a reason that they are always featured in horror movies.