Children showing high energy (9)
I believe the answer is:
offspring
'children' is the definition.
(I've seen this before)
'high energy' is the wordplay.
'high' becomes 'off' (I've seen this in other clues).
'energy' becomes 'spring' (as in having a spring in one's step).
'off'+'spring'='OFFSPRING'
'showing' is the link.
(Other definitions for offspring that I've seen before include "Progeny" , "Child" , "Young" , "seed" , "Kids" .)