The only thing I would suggest is that you get the children picked up from your home rather than school. It is one thing for a child to not be invited to a party, but another to effectively have the party waved under their noses. Might make it difficult for your DD when picking 6 friends and then returning to school.
Was just going to post exactly what Tombliboobs (great name) said. My niece wasn't invited to a party that involved a Limo picking up at school - she and others were quite upset and all of the parents were shocked that another mum could be so insensitive and showey-offey.