I think this should be a conversation for your husband to have with his parents. Although he may not want to, if he agrees with you it needs to come from him. He needs to let them know that you both greatly appreciate the generosity but the traditions and memories of holidays are more important than a lot of gifts. He needs to let them know that one or two gifts are more than enough. If they keep insisting then have them donate the rest of the money to charity or your son's college fund.