Ask HN: Any simple web apps for teaching kids?

Was recommended ba $10/mo app from my child's school (kindergarten) and was unhappy with how little it held the attention span of our 5 year old. So I stated working on a sight words app ( https://sn0n.github.io/sightwords/ ), about to add letters and numbers, along with shapes and colors (as a separate app, since it won't be just sight words at that point).

But my main question. Anyone else have links to other no install no ads no extras simple web apps for learning at a kindergarten level?