I actually wondered Bec whether anyone has been talking to him and being careful with his things now that your youngest is likely to be moving around more (ie don't leave your lego on the ground where the baby can get it, don't play with the beanbag zip the baby could choke...)? I know my DD1 (who is ten) went through a nervous nellie stage when our DD2 started crawling and it was because we were nagging her about making sure the baby was safe. Or have they been talking about safety at kindy/preschool? It wouldn't be hard for the whole question of 'safety/unsafety' to creep into his psyche.