Baby diapers and baby wipes cannot be purchased with food stamps.
If you're having trouble paying for diapers you might consider switching to cloth diapers which you can reuse over and over and even use the cloth diapers on other children.
They do cost some money upfront but once you buy them you won't have to buy diapers again.
If you can't do cloth diapers then you might check and see if your location has a diaper bank where if you provide details on your income and family then you might be able to get some free diapers through the diaper bank.