Omg they sound really thoughtless. I would be super peeved and can really understand your frustrations. I have similar issues with my in laws - they get ****ty when I bring good for my boys but don't cater for them. Well actually the last 2 times they have cooked them some sausages on BBQ (adults get steak). I don't have an answer other than to get a bit pre-emptive, which is what I ended up doing. I would just barge in with my own uncooked food and start using their kitchen and utensils etc and make a massive point of cooking for your boys but being really nice saying "oh no no please don't fuss for them, I'll cook their dinner, you're doing enough making us food!!!". Make a massive mess, put things back in the wrong place but do it all smiling and vague. If they are like my in laws that will completely freak them out and they may think about catering for your children!!! Just an idea lol or invite them for dinner, feed the kids at 5, make them wait until 8pm lmao. Sorry I'm really mean sometimes!