What is the best engineered toy for children?

I can only speak from a parent's perspective, not an engineering perspective.

* 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.

Not to be flippant, but a football is still my favorite toy decades after childhood.

Legos have excellent UX.