There are no quidelines, but I would want:
-certified personal trainer
-CPR & AED certified for children and adults
-additional certifications or continueing education on training youth
-experience or referrals from training youth
After all those things are met, I’d want to know if they had additional education for the specific reason I’m hiring them to work with my child. Specific sport training, conditioning, weight loss, flexibility, etc.
Good Luck in your search! I hope these provide you some quidelines.