I have seen it happen first hand where the man was doing what he could for his baby and the momma took him to court and he was told to pay less than what he was paying. But, I rather have it down on paper even if it is just $50 a month at least I know that I will get that $50 then if he decides to stop doing what he was doing. Then if he decides to stop paying the court ordered I have a recourse and can take him back to court.
See I agree that if he starts out "good", make him sign somethng..making it a legal written document so in case he does change you can take it to court but no reason to do that unless he gives you reason to IMO
and with all that has been said, all this ish is why I would never date/marry a dude with kids under 21.