I don't control how my kids play outside of safety, respect, and decorum.
I bought DS those sets of 100 interlocking blocks with Singapore math when he was 4. For 2 years, he and my daughter played mommy and baby blocks with them. There was some sort of rule about how the linked blocks break apart that determines when the baby blocks get fed and the mommy and daddy blocks have a new baby block. We also used them 2-3 times to illustrate regrouping in subtraction. Recently DS told me that he knows the answer to a math problem before he starts because he can see the size of the blocks needed for each number and the difference or what the sum would look like. That unstructured, not following the rules play, evidently contributed to building a fundamentally intuitive number sense without being taught.
