If you are looking for physical geography or earth science basics, Its not just for extreme geography for kids, its for everyone. This App has an introduction to the earth sciences that includes topics on the Earths structure, atmosphere, hydrosphere, and biosphere.
One big thing to remember... This kind of geography is not about countries and gross domestic products. Extreme geography is all about the Earth and the things that happen on Earth. Humans are only one part of the overall equation.