My brother would like to support his child but he would like it to be a court decision, not an agreement between his girlfriend and himself. He is concerned that his girlfriend may, one day ,deny any support

I helped my brother with this exact problem and he avoided paying back child support. He needs to go down to his local department of human resources and ask to see a case worker about signing up for childsupport. If the mother puts him on they automatically go back 2 years if the child is at least two years old or more and if the child is not 2 years old then count from the birth month until now and multiply that number by the amount that the court has awarded him to pay. And remember when you start in the whole they add interest, with interest alone my husband had to pay 8000 in interest. He started at 2000 in the whole and in 6 years he owed 14978 in childsupport and he paid he monthly payments. In 2010 my husband owed 14978 in childsupport noe he owes 3000 this comes from them taking his tax returns. Its in your brother best interest to sign himself up. Good luck

First he needs to file for legal visitation with the child in court, as part of it, he also files to pay child support, that is set though the courts.

He's right this should be done through the courts. He can file for custody and support.

... he would like it to be a court decision, not an agreement between his girlfriend and himself. He is concerned that his girlfriend may, one day ,deny any support

He might consider a stipulation between the mother and himself providing for the entry of an order for child support. Then file it with the court and ask for the entry of judgment on stipulation.