Medicaid will pay for and cover the cost of both adult diapers and children's sizes of diapers as long as a qualified physician diagnoses and prescribes the diapers for the adult or child.
If the diapers are for a child who is disabled or incontinent and needs diapers to help manage that incontinence or cannot be potty trained due to a disability then Medicaid will pay for those diapers.
The child must be over the age of 3 or 4 to get free diapers supplied to them through medicaid otherwise you will have to pay for the child's diapers out of pocket until the child reaches age 3 or 4 and it can vary in different states.
For an adult who needs adult diapers to manage their incontinence and cannot afford to buy them themselves then as long as a qualified doctor says they are needed then the adult diapers will be covered by Medicaid.
So you'll need your doctors prescription for the adult diapers or Youth diapers for Medicaid to pay for the cost of the diapers.