I found a great link on Parents.com with tons of great kid's party theme ideas and the how to's!
Check em' out!
"We’ve got loads of fun kid party ideas to get your creative juices flowing. Consider a party modeled after your child’s favorite board game: At a Twister-theme party, punch out polka dots from colored construction paper and stick them on your walls for the easiest decorations you’ll ever make. A Twister-licious cake features dots cut from rolled-out fruit chews!"