It is not free, but Tapestry has created an account for every child. Reach out to your child's teacher.
The website is free on a desktop/laptop. The app costs money. ABCYa has many engaging games to reenforce common core math standards.
Model with a 10 Frame
Magic Math Fingers
A Parents Guide to Rekenreks
Cardinality
Zero the Hero
How to Count Scattered and Circular Arrays with Manipulatives
By: Claire in the Excellent Elephants
How to Count Scattered and Circular Arrays on Paper
By: Zyaah' in the Excellent Elephants
Count to 100
Adding and Counting Strategy: One More
Subtracting and Counting Strategy: One Less
More Fewer Same
The Elephant Mass Song
More and Less
Number Partners to 10
Number Bonds
Hidden Partners