One of the most important things to look at is whether a toy allows the child to imagine, or if the toy does all the work itsef. When the toy takes over, children don’t learn and explore. A toy that is open-ended may look like one thing (a rainbow) but it can be used many ways to represent different things (a building, a bridge, a bed) and most of all, it enhances the child’s ideas and imagination, letting them build and learn in their own world.
We’ve always loved blocks and got our first sets of Grimms blocks when the kids were 3/newborn, and for years they’ve been loved and played with. In the last couple of years, we’ve added loose parts, peg people, and some wooden figures.