There really isn't many certifications in the U.S.
To participate with the USAG, as there is also the USAIGC, and one or two other doesn't require much in certifications. Taking the safety course and obtaining a professional membership is about it.
Look under education at usa gymnastics . org
USAG does provide Kindergym training ( KAT ) besides their Level 1 PDP program. There is also the Level 1-4 for women's. Bare in mind Levels 1-4 are considered developmental/recreational gymnastics levels.
There is also something called Gymcert. Currently they offer women's levels 1-3 and they have materials for levels 4, 5, and 6 and Boys.