If you don't mind the grumbles from the parents... a candy theme is always a great gender neutral party theme! You can pick a few colors to focus on or make it a rainbow of sugar!
Some ideas to add a little Frosting to a Candy theme...
Is your sweet tooth drooling yet? Love the fun colors and the multi-height banners! Source
Use over-sized lollipops to create a delicious centerpiece - add candy to a vase as filler and even string into garland! Source
Add fun candy details like these candy napkin rings - just glue candies onto a cut toilet tissue roll or wooden rings. Source and tutorial
Make paper candy toppers for your cupcakes. Source and tutorial