Mischievous brats ultimately admit mistakes (7)
I believe the answer is:
terrors
'mischievous brats' is the definition.
'terrors' can be an answer for 'brats' ('terror' can be a synonym of 'brat'). I am not certain of the 'mischievous' bit.
'ultimately admit mistakes' is the wordplay.
I cannot really understand how this works, but
'mistakes' could be 'errors' ('error' can be a synonym of 'mistake') and 'errors' is present in the answer.
A single letter 't' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for terrors that I've seen is " Great fears".)