DS (2.8) was with childminder from 11mo to about 17mo while I worked. Since then I've looked after him (maternity then quit work) & I had DD 10m ago. Last week he started preschool 3 mornings a week.
He's taken to it pretty quickly; 4th session had the breakthrough of 'I had fun at nursery today' in the car on the way home, but initially he was upset about going there, and when I left. He's a shrewd little thing and I'm sure he will be fully aware that I am going off with DD while he stays at nursery. The last couple of days he has taken to hurting her quite badly - yesterday he bit her twice on her hand; once on the nail/cuticle (drew blood 
) and once between the fingers (mark still visible this morning). I've been in the room or pottering when this has happened; I blame myself and for once I have managed a zen like calm and just taken him for time out every time he's done it.
He had a mate over yesterday and was a bit rough with her and her brother too - I had to give him time out for one of the 'attacks'.
Has anyone else noticed a sudden bout of this kind of sibling rivalry/bullying in a similar situation? If yes, does it last for ages and am I doing the right thing, or did anything else help your DC get over the phase?
Thanks!