Something popular with children, or the direct opposite (10)
I believe the answer is:
roundabout
'opposite' is the definition.
Both the definition and answer are adjectives. Maybe there's a link between them I don't understand?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for roundabout that I've seen before include "Circuitous" , "Ride" , "Traffic controller" , "Indirect" , "usually circulatory" .)