Well, here in DK the children will be addressed with informal you and sometimes with title by staff members.
As the adults themselves are addressed with informal you by those of the staff who work closest with them. i.e. secretaries, chief of courts and so on (except when the show is on of course) it is out of the question that staff would adress the children with formal you.
It's normal that the children are addressed alternatively with their name and title or just their name by some journalists when they are giving the little "interviews". But that's when the show is on. Example: "Prince Christian, was it fun to..."? The very same journalist may later, now that the formality is over, ask another question like this: "Christian, what do you think about..."?
That the children should be addressed in school as say "prince Christian" is nonsense. They are listed as "prince Christian" and so on.
In other words: The most formal thing the children will experience is to be addressed as "Prince Christian".
When they meet a cleaner, driver, cook whatever in the morning, that person may initially address them with a "Hi, Prince Christian" and then only "Christan" and that will especially apply to the older children, who can understand what a prince/ss really is.
I don't thnk the guards are required to present arms either should a royal child run past.
QMII and her sisters when they were children, had an idea about walking countless times past guards who were obliged to present arms. That little joke was ended with an admonishment and an order to the guards about not having to present arms when the girls walked by. That must have been in the early 1950's, so I doubt very much the guards do it now.
The thing about addressing children with HKH's, bow/curtsey to them and saying "sir" to small children, that I believe is Hollywood fiction. Must modern royal houses are much more informal.
