We trained our son at 2 by just sitting around the corner outside his room and putting him back each time he came out (after making sure he was Ok and comfortable and udnerstood our expectations, of course). He didn't get really upset, but he did persist in coming out! I think the first night it took about 4 hours and he came out over 150 times. By the third night he only came out a few times, and after a couple of weeks he never ever came out again. I would recommend this technique for any child who is old enough to understand. I have heard of a technique where you actually secure the door and leave, but we would definitely not feel comfortable with locking our child in.