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 !

This is ridiculous expecting a 5yo to eat spicy curry when some adults can’t even stomach it well. It might cause him the runs also. Your husband should have stepped in for your son. Anyway with your in-laws mindset to begin with, I think reasoning won’t work for them. It must have been hard for you. Hugs.