Is play better with natural materials?
Toys are not better than natural materials. But they are not inherently worse, either (setting aside arguments about sustainability).
The thing that makes an object interesting is the range of possibilities it offers. You can do a lot with clay or Lego. But an electronic toy that makes funny sounds when you press a button? Not so much.
Take a look at the mess in your child's bedroom. The best toys are used again and again in different contexts: in construction, in pretend play, in the bath. When I tidy my daughter's bedroom my instinct is to put all the doll's house toys in one basket, the blocks in another and the beads in a third. But as soon as she goes in there to play, it's all tipped onto the floor and she grabs whatever serves her purpose. The images on the 100 Toys blog celebrate beauty and order but we all know that that's not how our children's rooms look most of the time.
Toys as tools for thought
So here we are at the crux of it all: materials help us to think. If we are building and we want to span a gap between two towers we look around for something to form a bridge. That could be a log or a Lego baseplate.
When children encounter a novel problem, they first have to work through it physically. They have to turn over objects in their hands before they can turn them over in their minds.
The things we surround ourselves with matter. They help us think through problems. Better tools make for better thinking.
The link to schemas
When we play with materials in the natural environment, we are solving problems our ancestors would have encountered. How to bridge a gap, how to sharpen a stick, how to enclose a space. We must make do with the same resources: the things we find lying around.
And so we fall back on those building blocks of thought: schemas. Enclosing, rotating, positioning, enveloping.