Our three "middle" boys (7, 9, and almost 11) were captivated almost instantly by Jocko's The Way of the Warrior Kid book -- begged me to keep reading. We read 5 chapters and they wanted more.

The Tuttle Twins series is great for instilling the ideas of liberty, and I think these books may be great for instilling physical and mental strength. I tell them every day, "Get smart, get strong!"