I am looking for robot constructor general plastic parts

I do not know how call it, but I mean something like these pics:

Can I find something like this plastic parts in general or I must design them in solidworks and ordering for mold production by myself?

My goal is to build some educational robot kits for kids by this parts.

Like this?

Yes, but something has more parts. Also I couldn't understand what material the parts you put are made of?