Option to include a private note in all child tickets

I recently noticed a tick box when sending an email from a parent ticket, so a public note could be inserted into all child tickets.

What would be very useful is if we could have a private note that can be inserted into all child tickets.

I have a specific case in mind, where the main onboarding ticket could have a note added to show the user account has been created, so that the issuers of the hardware are aware that they are now able to make an appointment for issuing the hardware.

I am sure that there are many more situations that this would be useful