A.K.
Just so you know - Sunday the 11th is Mother's Day - so although the one responders idea is a good one - unfortunately it leaves you in a worse spot because then no one will come. I would suggest changing the date as much as it stinks. I would think that people have already started RSVP'ing to the other party and probably won't change their mind. I had a similar issue last year and I did the same thing...it was a hassle but we did it and we had LOTS of kids show up for his special day! I am probably a lot like the other kids mom and I send out invites VERY early because it seems like everyone's life is so busy that people need a lot of advance notice. Good luck!