Summertime birthdays are a great time to host a luau-themed party. A community pool would serve as an appropriate venue, or you could bring the beach vibe to your backyard. Party supply stores carry packs of leis for a few bucks each. If you have any tiki torches lying around, light them up for additional pizzazz or perhaps string up colorful lights around the party area.
For decor, go with bold, tropical colors such as bright orange, yellow and purple. Toss a drink umbrella in cups of fruity Hawaiian punch for a cute touch. Ask guests bring their swimsuits and a towel for wet and wild games, such as a water balloon toss, slip 'n' side and a hula hooping contest.