Have done an Artyparty myself for about 8 kids at home - bought stuff from BakerRoss (www.bakerross.co.uk) also did a cooking party - sent out invites attached to wooden spoons, printed out a couple of recipes, made aprons from pvc fabric as going home presents, we made cakes, biscuits and canapes for the adults to eat when they came to the "cafe" to collect. And no, it didn't just work for girls. Big tents are a godsend - beach party in our garden this weekend whether it rains or not - bbq, paddling pool for games and sand for hidden treasure - who says 10 year olds are sophisticated all the time!
Mermaids also worked well - got out all the xmas lights, bought some cheap treasure chest shaped boxes they decorated from Ikea and lined ceilings with net.