Small child's manoeuvre on bike? (4)
I believe the answer is:
skid
'manoeuvre on bike?' is the definition.
(skidding is a cycling manoeuvre)
'small child's' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'child' becomes 'kid' (synonyms).
's'+'kid'='SKID'
(Other definitions for skid that I've seen before include "Slip on wet ground" , "potential cause of accident" , "Slide uncontrollably" , "Slide sideways" , "Slide at an angle" .)