The greatest Abba hit, a children’s favourite? (3,4)
I believe the answer is:
ali baba
'hit a children's favourite?' is the definition.
I can't judge whether this definition defines the answer.
'the greatest abba' is the wordplay.
I cannot quite see how this works, but
an anagram of 'abba' is 'baba' which is present in the answer.
'the greatest' could be 'ali' (Muhammad Ali was known as the Greatest) and 'ali' is located in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for ali baba that I've seen before include "He discovered the magic words "Open Sesame"" , "Arabian Nights hero who discovered 'Open sesame'" , "1001 Nights hero" , "Pantomime character in contention with 40 thieves" , "Pantomime hero at odds with 40 thieves" .)