I am supposed to have custody of my children ever other weekend and one evenenig per week. Recently, my 7-year old son has been refusing to come with. I usually pick them up at their mother's house and he refuses to get in or stay in the car. Often he'll scream, kick, hit, and throw things at me. His mother provides no assistance. I suspect that she encourages this but have no proof. I also have two younger daughters to deal with at the same time, so it is difficult to spend alot of time "forcing" him while outside at their mother's house. Any suggestions, advice?