If the child has been born, he can file for paternity determination, a parenting schedule
and joint custody, if his. And he'll be ordered to pay CS.
Just a slight correction for MS.
MS doesn't have "parenting schedules."
MS also doesn't do joint physical custody. One parent must have physical, the other parent usually gets joint legal custody and standard visitation. Standard visitation in this state is every other weekend, every other holiday, and 6 weeks in the summer.
OP, Your son can plan to pay 14% of his adjusted gross income, which is gross minus taxes minus mandetory deductions for retirement and insurance.
Also, your son will be ordered to provide health insurance on the child, if it is available at a reasonable cost through his employer. MS Code defines reasonable as 5% of his AGI.
Your son needs to file a Complaint for Determination of Paternity and Establishment of Custody, Support, and Visitation. This will need to be filed at the Chancery Court for your county.
Your son also needs to prepare a Rule 81 Summons To A Date Certain. Before he files his complaint, he'll need to contact the court administrator for that county's Chancery Court and set the court date.
After filing the Rule 81 Summons and Complaint, he will need to have it served to her. If she also lives in MS, he will need to get personal service on her. The Sheriff's Dept. will do it for $25. Or you can use a private individual. It can be any individual over the age of 21 who is not a party to the action. Make sure they complete a service return to be filed with the court.
What county are you in?