I'm not sure if this is any good, but I remember using an older version years ago for research and it was really handy with accurate information, could be handy for kids. I'm not keen on downloading from sites, I believe you can also get a free version on iOS? Not quite sure though.
I thought £2.00 was really cheap for such a great software package.
My ipad is playing up and not letting me put the image on, apologies.