Ex won't keep kids and won't pay more support

We signed a separation agreement in April and it indicates that he keeps the kids six weeks over the summer. He is refusing to do so and refusing to pay any more child support. The summer is just now beginning so assuming he doesn’t keep the kids and doesn’t pay more support, do I take him to court and how long do I wait before doing so? After two weeks? After four weeks? After six weeks?

If he won’t abide by the custody terms, you should file a complaint for child custody and child support. That way, you can get an order that reflects the true custody arrangement as well as a support order that reflects the amount of care each of you is actually providing.