My in law invited us over for dinner. But she only cooked curry and white rice! My 5 years old boy don't take spicy food so I fed him before visiting my in law. However , my in law were not happy , saying that my boy don't appreciate her cooking (curry)! I was dumbfounded !
Does they know your boy can't take spicy food? If so, I believe kids is very honest and would say they can't take spicy. Say it in another way that you have try feed him before outside but he can't take it.