The most common and most likely answer to this crossword clue is the 6 plus 8 letter word TOILET TRAINING
I've seen this crossword clue in The Times
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Buddy explains!
The straight part
We know that "Child will be better at going after it" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case child will be better at going after it = toilet training.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TOILET TRAINING mean?
TOILET TRAINING verb- To train (a child) to use the toilet.
- To train (a domestic animal) to defecate and urinate in certain designated places.