Are they crafty? Usborne do a really nice introductory book on knitting, and you could include some pretty needles and nice cotton yarn for one of the projects
Lucinda Guy has also published a similar book which you can get at John Lewis. It is less pink and twinkly than the other one...
Is a carton of fine coloured powder that when mixed with water it turns to goo. Its great! Check ebay for it. If i was anygood at inserting links i would, but sorry am actually useless. I think its supposed to go in the bath but i will only be using ours outside in the paddling pool (will probobly need twice as much for a pool of water rather than a single bath though)
the 11yr olds down my way have no aversions to goo! We have had it once this year in the paddling pool and all the kids loved sliding down the garden slide (prob very dangerous - but had no injuries) and landing in the goo. Apart from one girl who doesnt like to get messy (very strange) i thought all kids liked to get messy, mine seem to make it their daily mission!
Photo printed Tshirts are good too. If you have digital (or can get ahold of) pictures of the two girls in question and get them printed onto Tshirts, is quite fun, especially if they are funny pctures. I had some distorted or warped before printing on just recently and they came out hilarious!