PONY League Rules

Can someone more knowledgeable than myself direct me to where I can find the balk rules for 10U. My son struck out the first batter and then the opposing coach complained about the way he was pitching. My son pitches from the stretch, so he stands straight up with his legs together, his right foot touching the rubber and his hands together. From there he lifts his left leg and delivers the pitch. Opposing coach was saying his legs have to be apart and he has to lean towards home as if he were getting a signal first, then bring his legs together, get set and pitch from there. The ump agreed with him and proceeded to call a balk on the next 5 batters because my son kept forgetting. I'm not familiar with the rules so just trying to educate myself. Any help would be appreciated. Thank you.