Lego Theme - A Lego construction party. I love the idea of supplying a little bit of fancy dress to each mini guests, rather than asking for full fancy dress. That way parents who can't afford it won't have to turn down the invite.
Lego Construction Birthday Party via Kara's Party Ideas
You don't have to be a Master Builder to master this LEGO Construction Worker Costume. It's instantaneously recognizable, easy to make,and comfortable to wear.