Its very early days and still lots of changes for them. Was the split amicable? It really helps if you and your ex can work together on this one, perhaps meet somewhere for a coffee altogether once a week so the kids can see you getting along still. I know thats not always possible and so soon after a split it may be too hard for you but think about giving it a go. It could be they don't want to talk because they don't want to upset you, kids get very protective of there parents at times like this, and have divided loyalties, so let them know its ok, but maybe they'd be happier talking to someone else, a teacher or perhaps a relative? The important thing is that they talk, it doesn't matter who to and you don't need to know what they've said unless its something damaging to them. I would fill the school in on the situation and ask them to find time to chat with the kids, they might have mentors that can help with this situation.