Product code Sims 4

I bought the sims 4 for my self, but my son likes to play sims also.  So I put it on is computer first.  I did not think anything of because we always used the same sims 3 games.  It is crazy if everyone will have to go out and buy another copy.  Well I was crazy because I was not going to us my son's username

 and password.  I paid 80 for my game the first time.  Good luck