K.F.
They are really too young to successfully wrestle without supervision. Teaching both children how to balance out the playing time would be the optimal situation. Perhaps they would do better with age appropriate action figures or trucks. Perhaps there is a fitness video they can both work on instead of having them wrestle.
Ultimately you set the stage and rules of engagement in your home. Ask the other boy if he no longer wants to come to your home because sometimes it could boil down to this. Also your son will have to learn how to deal with disappointments and so will the other little boy. Perhaps talking with the other mom to see what she suggests will also be helpful.
I hope this situation works itself out because it sounds like the other kid is trying to run and rule over your boy and that shouldn't be allowed to continue.