This year posed quite a challenge for us.  My twin sons, age 6, each chose their own separate party themes. One wanted a theme featuring frogs and the color green and the other wanted a water party where everyone would get soaked. I didn't want to have two completely separate parties so we compromised and they split a birthday party.  We started out by making two invitations (one titled "It's keen to be green!" and the other titled "Wet & Wild Birthday.") We then glued the backs of each invitation together so that the cards would open properly when the invitation was flipped over. The first invitation stated the frog party was to run from 1-2pm and that the guest should wear something green and bring a frog guest(stuffed, plastic, etc). The second invitation invited them to get soaked from 2-3pm and asked them to wear sunscreen, swimtrunks and bring a towel.  At the first party we played games such as leap frog and ate mini frog cupcakes and drank green punch. At the second party we played water games galore, ate blue Jell-O and sent home favors frozen in water balloons.