Have you ever watched 2 dogs play together? They will wrestle and run and then all of a sudden they just STOP. Then they start up again. This cycle repeats throughout the play session.

They do this to slow down the excitement, the stimulation. It helps them keep in control, and keep play AS play.

I suspect your son did not do this, and just kept going and going and going. In addition, he was likely yelling, laughing, providing verbal stimulation as well as the physical.

When playing with a dog, especially a puppy, it is imperative you follow the rules of the dog world.