Concrete is child's play to mix, vacuous lad conceded (8)
I believe the answer is:
physical
'concrete' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for physical that I've seen before include "hard work" , "of concrete structure" , "Having a material existence" , "Involving bodily contact" , "Bodily - material" .)