Children hand in tin (5)
I believe the answer is:
spawn
'children hand in tin' is the definition.
I can't judge whether this definition defines the answer.
'hand in tin' is the wordplay.
'hand' becomes 'paw' (synonyms).
'in' means one lot of letters goes inside another.
'tin' becomes 'Sn' (Sn is the chemical symbol for tin).
'paw' put into 'sn' is 'SPAWN'.
Can you help me to learn more?
(Other definitions for spawn that I've seen before include "Give rise to; fish egg" , "Product" , "Yield" , "Mass of eggs laid in water" , "Eggs deposited by amphibians" .)