From the facebook invitation:
"Swap 'til you drop!
Bring your LEGO minifig collection to show off, and swap with other kids (or grownups; that's cool!).
Enter to win a prize package of six Series 11 minifigs!
Take home a special LEGO-themed gift.
All ages are welcome to attend. Please RSVP and let us know how many people you're bringing so we can have enough gifts for everyone."