Tots are busy with a balloon, perhaps (8)
'balloon perhaps' is the definition.
'aerostat' can be an answer for 'balloon' (thesaurus). I'm not sure about the 'perhaps' bit.
'tots are busy with a' is the wordplay.
'busy with' indicates an anagram.
'totsare' with its letters mixed up with 'a' gives 'AEROSTAT'.
Can you help me to learn more?
(Another definition for aerostat that I've seen is "Hot-air balloon, airship".)