When I was about 9 my parents quite often weren't home when I got home from school, so we had our own key (my sister would have been about 12). One lovely, cold, winter's day when there was about 8 inches of snow on the ground... I was strolling home from school... throwing my key in the air and catching it. Until I wasn't catching it. And it went into the snow somewhere. And we couldn't find it
.
So we ended up camped out at one of my sister's friend's house until about 9pm
.
I also distinctly remember my dad getting us locked out once when I was maybe 7, and he posted me through a small window that was open so that I could open the back door. Heh. Dunno what his plan was going to be if the back door key hadn't been there...