My mum told me one that's kinda creepy.
When I was a baby, maybe about 6 months old, she put me into my cot to sleep one afternoon. It was a high sided wooden thing with a drop side for access that required you to press in 2 little nubs, one each corner to release the side.
She came upstairs and found me outside the cot, asleep in the middle of the floor about 2 metres from the cot. The sides were up, there is no way I could have opened it, I couldn't stand and the sides were far too high to jump over.
Apparently she never felt comfortable leaving me in the room after that.
Also. When my younger brother was born he was put into that room as his bedroom. One evening me and my mum were on her bed playing with my brother who was about 1 year old and we heard this noise coming from his room.
Panicked my mum went to look and one of his musical toys was in the cot playing to itself despite not being activated.