Brace yourself. This year we've had a round of 4 y.o. parties and every single one of them (without exception) has been maccas/HJ's.

I loathe them. The food is usually nuggets/hamburger with chips and the nominated softdrink (just watch this because they do happily serve coke to kids this age). Followed by a lurid-coloured icecream cake. Missy E usually picks at the food, drinks all the fizzy drink then enjoys playing on the equipment. So I've come to accept that's what the experience is about for her. Like others said, the food served up at play centres and even at home parties can be just as bad. Yes an association forms with the brand, like it does with all the brands in our lives, it's about how you live the other 99% of your time. The weight you put on brands etc right across your whole life will determine how much your child is influenced by them.

Socially, it's not necessary to explain why you're not attending, just a polite 'sorry we can't make it this time' will do. And FWIW yes I do think you have the right to censor his experience at this age, in the same way you might choose to limit his television viewing or keep him away from other environments that you don't feel are developmentally appropriate.