Legal Question in Family Law in California

If you can establish a contract, rather than a gratuitious promise, then you can. The trouble is establishing what consideration you gave for his agreement to pay the college expenses. If you did not give anything in return, then you would have to show some form of fraud or detremental reliance. For example, if your child got into Cal State and USC, but you couldn't afford USC. Then the dad said "go a head and enroll at USC, I'll make up the difference" that would at least give a colorable claim to an enforceable promise because you relied on it to your financial detriment. But "You really aught to contribute to Jr's education" "Oh, OK, I'll pay $$ per month," will not support a legal action.