Education.com has a huge database of free worksheets and printables for kids, and they are also offering access to some at-home learning resources for free during school closures.
Great Schools.org has free worksheets for children from preschool through grade 5.
And if you need a touch of whimsy, check out these printable activities from Click, Clack, Books, home of the amazing book series by Doreen Cronin and Betsy Lewin.