I believe it depends on his income, etc. They have child support calculators on the state websites. It may also factor in your income, I can't say for sure on that part. It doesn't seem that great for 4 kids though unless y'all make a hefty amount. That's messed up he won't help out anything extra, my daughter's father is a dead beat as far as being in her life but he still talks to me (why he doesn't talk to her I don't know, I've got onto him about it before) but he will help out when he can. For one child our court-ordered child support, according to the state's child support calculator, was $430 for ONE child! That was an USMC E-3 salary with BAH (based on the zip code for yuma arizona if you want to look the pay chart and BAH calculator up and compare it to your ex's salary) so not sure how close your ex's salary is to that, you could look up your state and find the calculator b/c that sounds silly for all 4 kids.
Not sure how to advise about the boat rocking thing, that is something that you have to trust your gut with. Maybe break it down barney style for him and tell him the $600 a month doesn't pay for blah, blah, and blah for the 4 kids. Child support is not meant to cover a majority of expenses, but it should cover near half if not close... it took two to make them and both should be responsible in some way.