I don't know why you have got such a hard time, you made a massive effort to set of at 4.30am, which I wouldn't do for anyone, and they can't even be bothered to go to the park when you get there but moan if the children are boisterous in the house.
I don't see what you have done wrong except have a moan. Even the sausages, you cooked your own and ate the rest of the stuff, I don't think that's rude, I have a friend whose son has never eaten a meal ever in my house and only eats bread and butter, I don't care!
Basically, some people are good hosts and some are not. When I go to my mum's house, she immediately stops what she's doing and takes the kids out with her somewhere as she loves to be with them, plus asks what food to cook so we all agree and are happy before we start.
They aren't great hosts, however much everyone goes on about it being polite to eat what you are given. This feels like a different age.
If you don't have fun with people (going to the park) and have to eat food you don't like and get told off a lot, the children simply won't like going there, even if you make them and I'd hate for my grandchildren to dislike coming to see me.