I feel for ya on your situation. Women can be fucked up. I wish you and your kids all the best.
Thought I would give you a little info from experiences with child support. Shit I should know a little I've been paying it since I was 15.
She will get hers when the time comes. Were I'm at the CSA are all Nazis. They will throw you in jail, take your drivers licence, and take your tax return to pay back child support. They should go back to the day you split with your ex and make her pay from their. So she will start out being behind. Again this is from were I'm at, they will only let you miss 1 payment before they are looking for you. If they can't find you there will be a warrent. I know ppl that had to run from a child support warrent like it was a murder rap.