The most common and most likely answer to this crossword clue is the 7 letter word URCHINS
U
R
C
H
I
N
S
Buddy explains!

The straight part
We know that "brats" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case brats = urchins.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 URCHINS mean?
URCHINS noun- A mischievous child.
- A street urchin, a child who lives, or spends most of their time, in the streets.
- A sea urchin.
- One of a pair in a series of small card cylinders arranged around a carding drum; so called from its fancied resemblance to the hedgehog.
- A neutron-generating device that triggered the nuclear detonation of the earliest plutonium atomic bombs.
- A hedgehog.
- A mischievous elf supposed sometimes to take the form of a hedgehog.