I have no idea if its easier or harder for grown vs younger children. My guess is that they are just two completely different things.
What I do know is that at your children's age, they can "own" the relationship with their Dad (and he with them). With younger children, I think that there are moments when you have to advocate on their behalf. And I will say that with younger kids you do have to deal with the fact that you will have diminished time with them through no choice of your own, and that has been a bitter pill to swallow.
I think you are right to gently encourage them to have a relationship with their Dad. If he were wise he would try to establish some sort of relationship with them, without OW at first. Regardless - he will have to figure it out with them.
