I've wondered about that. Most candidates with young children aren't keeping them on the campaign trail with them. Why isn't Heidi home with the kids, if they don't have a better solution to keep their lives as normal as possible?
My guesses:
1) She has a job outside of the home
2) The parents and kids thought it would be fun to have them on the campaign trail and good to show a happy family
3) It has been harder than all of them realized it would be