I have two kids, 10 & 12, and I'd like to provide them with some math homework that is at least somewhat tracking their current and upcoming "Common Core" work. The school isn't assigning any homework, and I am disappointed at how thin their knowledge of the topics is despite getting good grades. The market, both online and in print, is awash with material, but much of it is really poor quality. Often it is trying way too hard to put some new/cute/fun spin on topics that really just need pen, paper, and practice. So many videos, contrived stories, artwork, ... my kid is 12, not 5.
Looking for any sites or book series folks have found useful. Ideally, these would be printable since they have to show their work on tests and are quite weak at this, especially with so much of their work exclusively on Chromebooks.
I recommend getting some math olympiad books; at that level they're just like puzzles so should be fun.
https://artofproblemsolving.com/wiki/index.php/Olympiad_book...
Go for general problem books (non-topic-specific), and start with the easiest problems that they find fun.
I remember the following two books were interesting (though might be somewhat harder). You might find them on the internet archive or pdf's online.
Challenging Mathematical Problems With Elementary Solutions (Volume I, Combinatorial Analysis and Probability Theory) - A. M. Yaglom, I. M. Yaglom.
Challenging Mathematical Problems With Elementary Solutions (Volume II, Problem From Various Branches of Mathematics) - A. M. Yaglom, I. M. Yaglom.
Additionally, look into various olympiads:
American AMC 8 and AMC 10 from various years should be easiest:
https://artofproblemsolving.com/wiki/index.php/AMC_Problems_...
And when they feel adventurous, take a look at contests. Some countries (e.g. Romania, Russia) have contests for lower grades, though they are still quite difficult.
https://artofproblemsolving.com/community/c3754998_aops_year...