Promises second child will get stuck into cereal (5)
I believe the answer is:
oaths
'promises second child' is the definition.
'oaths' can be an answer for 'promises' (I've seen this in another clue). I'm unsure of the 'second child' bit.
'stuck into cereal' is the wordplay.
'stuck' becomes 'h' (I can't justify this - if you can you should believe this answer much more).
'into' means one lot of letters goes inside another.
'cereal' becomes 'oats' (type of cereal).
'h' placed inside 'oats' is 'OATHS'.
'will get' acts as a link.
Can you help me to learn more?
(Other definitions for oaths that I've seen before include "Swearwords" , "Solemn promises or curses" , "Imprecations" , "Swear words" , "professions of loyalty" .)