Or maybe they don't want to go to their father's for visitation. They don't want to leave the car, so they refuse to go. Then the Mom gets in trouble. And they trust what their parents say, but they also go by their instincts, knowing that their Dad is a scary guy. Even if the parents are separated, it sounds as if the kids can still be victims.
Most dads have visitations rights, which can really confuse the kids.
In the children's groups we talk a lot about visitation and what it's like to see their dad. They usually come back from visitations really wired up and having a lot of different feelings, and they act those feelings out in different ways. Sometimes they come back upset and angry. When they color, they color really hard on the paper, with jagged edges, and make scary pictures. They don't get along well with the group leaders or the other kids.