Younger sib copying elder sib's behaviour problems

[PrettyCandlesAndTinselToo]

What do you do when a younger dc is copying an elder dc's behavioural problems?

Pray?

I wouldn't describe the words I use when it all gets a bit too much for me as 'prayer'. No, not even though they are uttered in a beseeching tone and include the Name.

But seriously, what do you do?

Younger is more likely to do it when elder is not around.