Jeremy Silman's books are great for beginner/intermediate strategy after they've read a few of the total beginner books. How to Reassess Your Chess & The workb

Jeremy Silman's books are great for beginner/intermediate strategy after they've read a few of the total beginner books. How to Reassess Your Chess & The workbook Complete Book to Chess Strategy are both good. They might be a little heavy for a 7 year old but with some guidance I think they're doable. I think I read them when I was 9 or 10 and didn't have any trouble. Chess.com lessons are really good too and might even be a better place to start. chess master 10 had a great walkthrough tutorial on strategy by josh watzkin that i did around that age, if you can find a copy of it