This sure is a surprise!
Mary talked a little about it today in France:
https://www.bt.dk/royale/mary-derfor-sender-vi-vores-boern-til-schweiz
When asked about sending the chidlren to Switzerland, she replied:
Vi ser det som en gave til vores børn, hvor de kan være sammen om det, og en gave de kan have med sig resten af livet,«
"We view it as a gift to our children, where they can be together about it and a gift they can share/bring with them for the rest of the life."
All reports coming talks about a short stay. Presumably anything from a few weeks up to three months or so.
It is of course not unusual that royal children are send away for periods at least. And Christian is about the age that J&F were when they were send off to a boarding school in France for a year.
That was a very difficult year for not least Frederik. The education was on a higher level than back in DK, so Frederik in particular struggled with Latin.
Nor is is unusual in royal/traditional noble circles to send the children out into the world to study once they are in their teens. The traditional formative journey.
I wonder if this is a test-run for the children. They will in this way, and fairly gently, learn how it is to go to school abroad, without mom and dad around the corner. Here they will support each other - and I think as a consequence of that, grew even closer. Even if this is only for a short period.
Anyway, if this is something some of the children find interesting, say Christian and Josephine. Then M&F can already now start to look for suitable schools abroad. And if say Isabella is less keen, she may need a few more years before she will again contemplate studying abroad, say after high school.
And say Vincent hate every minute of this. Then they know he is better of studying at home in DK.
It will be interesting to learn more details.