Ask HN: What is the best engineered toy for children?
The best way to learn the principles of design is to see them in action.
* Melissa & Doug toys are robust. In particular, the cars and trucks take the same beating as the other toys and have never broken. They're relatively inexpensive and can be found in department stores like Kohl's.
* Mega Bloks, basically giant Legos, are also robust. They get stepped on, sat on, dropped, kicked and thrown, and they all still fit together. I don't think they're as tough as actual Legos, but they don't hurt nearly as much when stepped on.
But a ball is universal. You can throw it, kick it, roll it, chase it, hit it with a stick. The kids will fight over the ball. You put it in a parking lot or an empty field and they'll find something to do with it.
You can put a can on the ground and throw/kick the ball and see who hits it. It needs a surprising amount of skill. And when that gets too easy, you can have someone whose role is to block the ball from hitting the can.