Reddit mentions of Combination Challenge

DogDay and DWChandler have two great recommendations. Absolutely do both of those things.

Also, I'd suggest getting a chess board, buy a big book of chess puzzles (preferably with solutions) and set up the board every day with one of the chess puzzles. Go over it together and try to work out the solution. Then, at the end of the day, go over the real solution. See how you did and see if you can understand why the solution works.

Finally, just play games with him. It's okay if he doesn't play master level chess. It's more important that he has fun to start with and it doesn't feel like work. Encouragement is important.

I'm not sure what to recommend for a book. I haven't tried this one but I own the harder version (Combination Challenge) and it's a pretty decent collection of puzzles.