You do need a perscription from either your kids doctor or urologist in order for Medicaid to pay for them (at least in Washington State, that's the rules for baby and adult diapers). I'm not sure about wipes, since I have been told by my insurance that they don't cover them (we use the cloth wipes mostly anyway).
Once you have the perscription, you can go to a local medical supply shop or one that delivers them to your home. I go through CCS Medical for both my stuff and Angela's stuff every month (catheters, ostomy supplies, gloves, bedpads, pull-ups and adult diapers).
Here's a list of other mail-order medical suppliers:
Hope this helps you out!
(single mommy to Angela, 3 years
:and Emma, our angel in heaven
We are a pro-nursing family!