PBS Parents: Website with readable articles about mathematical development in children, activities and games to do at home, and help for parents.
That’s Math: Conversation starters about math for many ages.
Adding Math, Subtracting Tension: Books for parents of younger children and older children published by the National Council of Teachers of Mathematics. Math activities for parents and children to do together.
Pinterest: All sorts of math activities from parents, homeschoolers, and early education teachers. Follow my Pinterest board.