For a birthday your girls will LOVE, try an iNail party...
We rented an iNail machine for my daughter's birthday party. Girls can do their nails by themselves using the automatic manicuring machine called iNail. It can print high quality art designs on your nails. We had a blast and all the girls had a lot of fun.
thats pretty cool although its probably really expensive. its also not the same as getting your nails done at an actual spa! i guess its ok! but thumbs up for originality!