Wood residues instead of predefined blocks
It must be not always predefined blocks!
Why don’t the carpenters ask, whether wood residues are to give away or to acquire cheap?
Or go in the forest, park or similar and collect the logs, tree branches, etc.
The wood remains stimulate not only the creativity of construction, but invite the children to operate artistically. Among others they can paste over the wood, paint, draw with patterns and carve.
Specially manufactured things, also toys, get more appreciation, they are treated more carefully, and at the same time, they learn that you don’t have to buy everything.