Some present ideas please

[blibblibs]

I have to buy a gift for a 10 year old girl and a 8 year old boy. Budget is £10 each, £15 at a push and I need to be able to buy it from Amazon.
I know they both like Lego but don't want to buy them any sets as they have so many i'm bound to get it wrong. Not sure of any other interests. Any help will be most appreciated

Books? Some game they can share like think words or something similar?

Things I have bought for my 8 year old ds on Amazon within budget:
Chill factor slushie cup
200 piece jigsaw
Lego technics plane
We detectives game
Strange but true book

Can't help with the girl much, but I loved anything craft based at that age.

You could have a search on Amazon for Klutz, they do lots of very good craft / construction books suitable for their age, within your budget, with some Lego related such as this one.