Tablet for a wild animal loving 7 year old- kids fire or other?

[Acunningruse]

DS is crazy about animals, loves the National Geographic kids website and stuff on You tube and his favourite thing is to have me Google 'which is the fastest/biggest/whatever animal'. He might use spelling/maths apps but wouldn't watch films on it.

Which is the best tablet for him? I like the idea of the Amazon kids Fire having (as I understand it) the best parental controls and a child friendly interface. But is it necessary/worth the extra money over a standard tablet?

Budget is less than £100 so iPad is out but he is used to using my iPhone and our iPad.

Thanks

personally i would look for a second hand ipad. music magpie are currently selling a second hand one here at £74.99. It is 'locked' to vodafone, and i dont think you would have to unlock it because you will just want to use wifi (best check this though! i think it is free to unlock it from vodafone anyway)