Rebuke first children going to conceal themselves (5)
I believe the answer is:
chide
'rebuke' is the definition.
(I know that rebuke can be written as chide)
'first children going to conceal themselves' is the wordplay.
'first children' becomes 'c' (hst letter of 'children').
'going to' means one lot of letters go next to another.
'conceal themselves' becomes 'hide' (I can't justify this - if you can you should give a lot more credence to this answer).
'c'+'hide'='CHIDE'
Can you help me to learn more?
(Other definitions for chide that I've seen before include "Censure, berate" , "lecture" , "Tell off" , "Seeing scold" , "Reprove" .)