In any court case to determine child support needs and obligations where the alleged father of the child is less than 18 years old, the parents of the alleged father shall be made parties to the case. If the mother is also less than 18 years old, the mother’s parents shall also be made parties to the case. The parents of the alleged father (if he is found to be the father, of course) and the parents of the mother may be jointly liable for the support of the grandchild until both of the grandchild’s parents turn 18.
In determining the amount of child support to be paid, the court may consider “in-kind support” (presumably things like providing child care, diapers and food). The court may also consider the standard of living and circumstances of the paternal grandparents; the relative financial circumstances of the maternal and paternal grandparents if both parents are under 18 and the responsibility of the maternal and paternal grandparents for other children under 18.
In any event, the amount of child support cannot exceed the amount of the standard of need for one person under the Missouri.
The applicable law is §537.045 of the Missouri Revised Statutes.
If you find yourself in this situation, consult and experienced Missouri family law attorney.