Beach balls when deflated fit in a standard envelope and when inflated reveal all the party information. Kids don't really care about a piece of paper, it's having fun they like, so sending something to goof around with is far more exciting, though not as easy to hang on the refrigerator.
Likewise, small frisbees were sent in cd sleeves with hand punched circles that had been written on by the birthday boy and addressed to each attendee. Both ideas truly set the vibe for a fun filled party. What other small items would work for this purpose? Leave your ideas in the comments below!
(Image: Martha Stewart Crafts Dept.)