DD was about 15 mths and moved because we needed the cot a few months later. Easy transition, we had the bed in with her cot for a while and she started off wanting day sleeps there then went to night sleeps.

DS is still in his cot at just over 2. He can't climb out because the mattress is at it's lowest point and he doesn't really try unless the rail guard is down. It is nearly time though, we find him in all sorts of weird positions with his legs hanging out and head pushing up on the rails. He sleeps so well now - from 7-6 without a worry so I am hoping that won't change!

ETA: We didn't actually put the bed IN with her cot