8-10 year old girls are starting to want to be girly. Or increasing in their girliness if they've always had a thing for pink and dresses. Even if they're neither of those things normally I think they would like some pink nail polish and lipstick. Go on, let them. It's Christmas.
Try The $2 Shop for some nice cheap stuff. 'Cheap' makes it sound horrible, but they have cocoa butter lip balm at The $2 Shop, so just because it's cheap doesn't have to mean it's nasty. I was a real tomboy growing up. We lived on a pseudo-farm. But I would have loved to have been given this when I was 8-10.
This one was a stretch for me. I'm not very in tune with the 8-10 year old boy psyche, never having been one, raised one or taught one. But I think a good old yo-yo might fit in nice here.
I had one around this age I think. They were really cool. It was fun to learn new tricks. I had a budgo version ,which worked just as well as the Pro-yo's and other expensive yo-yo's out there, but mine was unique so I made people think it was cooler. And it lasted the yards just as any other. I had it for years until I threw it out, I think when I was moving out of home. I'd suggest looking at (you guessed it!) The $2 Shop for one.