A really fun theme to do is Monsters! Look at the stored (but still fresh!) frosting from before, too - here
Start with a fun invite! I love all the different monsters and colors! Really gives you a lot to work with for the party! Source
How cute is this tissue box?!? These would be fun as decorations or for an activity for the kids to do! Source and tutorial
Another favor or activity for the kids would be these silly bookmarks! Source and tutorial
How about a few of these funny monster heads for decoration...and a lift! Source and tutorial
Finish off with silly cupcakes! Source and tutorial