The most common and most likely answer to this crossword clue is the 7 letter word CRAWLER
I've seen this crossword clue in The Guardian
C
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More clues leading to the result CRAWLER
Buddy explains!

The straight part
We know that "One pandering/active baby" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one pandering/active baby = crawler.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 CRAWLER mean?
CRAWLER noun- A person who is abused, physically or verbally, and returns to the abuser a supplicant.
- A sycophant.
- A child who is able to creep using his hands and knees but is not able to walk.
- A crawl swimmer.
- A tractor crawler, a motorized vehicle that uses caterpillar tracks instead of wheels.
- A software bot that autonomously follows connected paths such as webpage links.
- A mobile stage in the development of stationary hemipteran insects such as scale insects- generally the first instar