My step-son's birthday is April 17th, Amelia's April 21st. I figured with birthdays so close together it would make for one BIG birthday. Rent a bouncy castle kind of thing. Thomas loves bouncy castles... and has not a clue what a birthday is (his is in January). I'm sure once they're older they want their own thing. Ofcourse, my step-son gets a party at his mom's house too, so it wouldn't be that big a deal.
My birthday is August 30th, DH is August 27th. I always told him we should get married inbetween and call it celebration week. Nice and easy once the kids are grown, only have to get off one week a year to celebrate everything

(DH lost his first child on August 26th. Born at 20 weeks)