The most common and most likely answer to this crossword clue is the 5 letter word DOGGY
I've seen this crossword clue in The Times
D
O
G
G
Y
Buddy explains!

The straight part
We know that "Pet for children" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pet for children = doggy.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 DOGGY mean?
DOGGY noun- A dog, especially a small one.
- Doggy style
- (armed services) A junior temporarily assigned to do minor duties for a senior; a gofer.
- Suggestive of or in the manner of a dog.
- Fond of dogs.