If you really believe it's over, then you both should be mature and agree to be civil for the kids sake. Playing hardball and getting revenge only makes it worse for all concerned - taking his car means he won't be able to go to work and give you child support. You also should get a custody agreement so you both don't end up using the kids as pawns. The kids still need to have their father in their lives, so please always remember that.

If things turn around and you both decide to stay together, then you should get couples counseling. There's also many good 'fighting fairly' websites. A break up doesn't have to be ugly. I love this quote: "love your kids more than you hate your ex". I'm sorry you're in such emotional pain.