Mathgames.com is great. It has math practice by grades, by skill, and math games as well.
I haven’t checked it out yet, but scholastic.com has programs for free right now due to the virus situation.
https://classroommagazines.scholastic.com/support/learnathome.html There are so many wonderful educational apps! Many are free or low cost.
Books from the library to be read on kindle or kindle apps.
Homeschoolers already have the free resources figured out. Google homeschooling blogs and I’m sure you will find plenty of ideas and recommendations.
Educational YouTube videos. You can learn everything on YouTube!