DS 15 months has started the habit of weeing most times when I change his nappy. I use terry squares, so now keep the old one over his willy for a few seconds when changing it to try and catch any sudden wee. MIL says it's just the sudden rush of cold air to his bottom, which causes a shock reaction, and that it used to happen when she changed DH nappy, and on one occasion he nearly put the living room fire out (lol)! I'm not so sure, and wondered whether it was normal?