I'm currently reading "Mathematics: From the Birth of Numbers by Jan Gullberg" with my 3 sons (16, 12 and 10), and by taking it slow (one minor number per day) with lots of work together its helping build things up for them from first principles.

I read it myself years ago and it was a great and entertaining way to fill in the gaps from my meager math education.

https://www.goodreads.com/book/show/383087.Mathematics