This is a book for kids around 9-12 about 2 siblings who get accidentally sent back in time to various times (4 million years ago, 2 million years ago, 1 million years ago, etc.) and experience what it would be like to live during that time. That have to use their knowledge and wits to stay alive and make friends with the natives, if at all possible. I'm looking for pencil-type drawings. The kids are my grandkids, so I want the drawings to look like them.