What babies do — bit by bit? (6)
I believe the answer is:
teethe
'what babies do' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for teethe that I've seen before include "Develop gnashers" , "Have initial trouble (as a baby?)" , "Experience growing pains" , "Cut one's first dentition" , "Develop incisors, say" .)