If I cash out my 401k plan, can child support take it?

Child support can take it if its not in a deferred income plan (retirement plan). In addition, you will have tax consequences and a penalty depending on your age. It doesn't make sense to cash out a retirement plan. You can roll it over into a roll over IRA without any consequences.

If your behind in your payments and they become aware of it, then they will file to get it;