Children entertaining grandpa arranged flowers (11)
I believe the answer is:
snapdragons
'flowers' is the definition.
(snapdragon is a kind of flower)
'children entertaining grandpa arranged' is the wordplay.
'children' becomes 'sons' (son is a kind of child).
'entertaining' is an insertion indicator.
'arranged' indicates an anagram.
'grandpa' anagrammed gives 'napdrag'.
'sons' placed around 'napdrag' is 'SNAPDRAGONS'.
(Other definitions for snapdragons that I've seen before include "bloomers" , "Flowers" .)