We're having two parties, one at "home," where my husband and I grew up, and one here for her little friends. Since the "home" party will be mostly adults, I didn't really do an over-the-top "theme" but more of a color scheme that matches the outfit she will wear :-)
Here's how my DIY invites turned out:
Front
Inside: (I saw a card in a store hinged like that and fell in LOVE with it!)