critical play(s) -- mental growth(s)
_ .. / machine(s) / art(s) / change(s) / human(s) / world(s) / _ / .
play ... a primary indicator of (...) mental growth
play enables children to progress along the developmental sequence from the sensimotor intelligence of infancy to pre-operational thought in the pre-school year to the concrete operational thinking exhibited by primary school children ... ... play also serves important functions in (...) physical, emotional and social development(s)!
