My dd is five and in year 1. She is a very confident, gregarious little girl with lots of friends, and she gets invited to plenty of parties, playdates etc, so she doesn't miss out overall. However, in the last few months, she has started to identify one little girl in her class in particular as her "best friend", and the feeling seems to be fairly mutual.
She is really eager to invite this little girl to our house and in fact, we have invited her a few times, but the parents of the child in question do not allow any of their seven children to go for playdates, birthday parties etc - they seem to have a very busy family life which revolves around church, kumon and loads of extra-curricular activities.
I respect the right of the parents to bring up their kids in whatever way they see fit, even if I don't agree with it, but my little girl is finding this really hard to deal with, and has been quite tearful about this recently. She also keeps talking about how "mean" her friend's mummy is - I want to discourage this, but secretly I can't help feeling a bit the same way! 
Any tips as to how I can help her deal with this?