I strongly hope that I am wrong, but...
It looks like unvaccinated children will also need a negative test when they return by plane to Switzerland from 26 June onwards.
at least my understanding is that EVERYONE, including children will only be allowed to return by plane to Switzerland with a negative test. (Rule 13 in the linked doc has no exceptions)
Children up to 16 will however be allowed to enter Switzerland without a test. (Rule 16 in the attached doc). That may apply for entry via train or car, But it does not help if they cannot board.
Link to new rules from 26 June
That would be a lot worse than the current status, where Children under 16 are exempt from testing for boarding and entry to Switzerland. (Unless coming from a variant country)
update: it looks like this document is being edited by the respective department. It's still not clear, but likely not yet final. Please hold on...