I used to love the idea of being a squire when I was a kid. I read a lot of books about it, although mostly fiction books.
One really good series for girls who are interested in this kind of thing are The Song of the Lioness series by Tamora Pierce.
This is a series of four books that follow a girl who pretends to be a boy so she can train as a knight. It's the first series in a bigger group of books based in that world.
It goes into detail about the training she has to do, like different kinds of fighting, literacy, government and history, horse riding, marksmanship and so on.
I loved these books and maybe your kids will love them too.