Well I personally know that two year olds are pretty smart... I know for a fact my brother in law definitely knew how to unlock not only the doorknob but also the deadbolt by the time he was two and would regularly sneak outside the house. I don't own children, but I have been around them enough to know that you can blink and they'll be gone. They are smart and fast little buggers.

It's a shame that this happened, but there are so many factors. The mother was sleeping, it wasn't like she was on the phone or playing on the computer or some other sort of activity that should not have had preference over watching her child. If a mother can't sleep...

I just feel awful for both the child AND his mother

I know when I finally have children, I will have locks on the doors like the ones described are are way too high for a young child to reach (incidentally, my parents also had a similar lock installed on their kitchen pantry door to prevent my sister from sneaking into it and stealing food and candy when she was younger... lol. My other sister and I caught on fast and would end up locking her inside it... we were evil children, I'll admit).