LMAO...are you kidding me? A three year old can't open the door? Mine sure did!
Our 3 year old fell asleep in our teenagers room last July on the Dream. Our son was 17, and watching his baby brother, so my husband and I could have a night at the Steak House. When we returned, our older son said he was exhausted and was staying in the room, since our 3 year old was asleep, why not just leave him there.
Around 3 in the morning, I heard crying. (I am a light sleeper, and figured my 3 year old woke up, couldn't find my husband or myself and started crying. I went to go get him from the older boys room, and guess what? I opened the door and he was standing right there in the hallway. NOT only did he open a locked door, but he did so in the dark. Interior room...you know how dark they can be! Luckily he was so confused, he didn't go anywhere.
So, while I don't know about the OP here, it can certainly happen. I didn't think he woudl be able to open the door, they are heavy, and he is usually such a sound sleeper, but after that (and yes, my heart was pouding!) he was always in our room, even if we had to carry him over from his older brothers' room.