You have full custody? It ain't worth it to them, I know from experience! Especially sense they do not know their mom at all. The 12yr old has full right to do so, but the 9yr old can not make this decision yet, this of coarse is if you guys did everything legally. What I would do, if you have full custody is let them stay with her for like a month or two during the summer or something. Then let them decide what they wanna do. Don't let them do it cold turkey. You have to know that their mother has been talking them into them asking you to do this. It sucks that she is using the kids. You may want to do all go to dinner and discuss this. See what the kids really feel with both of you there. I was always used as a middle man to get what either parent wanted, I am taking a pretty good strong guess that the mother is doing the same thing. If they do go over to her house, and stay there most of the time, and you get the weekends, DO NOT LET THEM TAKE ANYTHING FROM YOUR HOUSE TO HER HOUSE. Games, computers, cell phones, gameboy, board games, toys, etc. Only allow them to take their hygiene products, school material and cloths.