J.P.
For the 6 year old I would suggest: Littlest Pet Shop or Polly Pockets - both you can get some fun little things for $5 at Wal-Mart. Especially since you are puchasing from boys those are "safe" gifts! :-) Books are also a great idea at any age - for the 6 year old I would Junie B Jones or Pony Pals would be fun ones for her to get. Good Luck!