Clasp to secure tot’s protective covering (8)
I believe the answer is:
cladding
'protective covering' is the definition.
(cladding is a kind of protective covering)
'clasp to secure tot's' is the wordplay.
'clasp' becomes 'cling' (I can't explain this - if you can you should believe this answer much more).
'to secure' is an insertion indicator (inserted letters are secured inside).
'tot' becomes 'add' (synonyms).
'cling' placed around 'add' is 'CLADDING'.
Can you help me to learn more?
(Other definitions for cladding that I've seen before include "protective outer covering" , "protection" , "insulating layer" , "Covering material" , "Protective covering on a building" .)