The first one we read was The River of Grace: A Story of John Calvin. We then read The Ocean of Truth: The Story of Sir Isaac Newton, and we are currently reading A Piece of the Mountain: The Story of Blaise Pascal.
Biographies are a great means of teaching, learning history, etc. Yet I also think of these kinds of Christian biographies as an opportunity to help our children to set their hope in God and not forget his works (Ps 78:5-8). Those who understand history well (Prov 9:10) will have their eyes opened to see God at work all the time.