Re: What to do with the kids during school holidays
We sent them to one of the Stiftung Zurcher Schulerferien holiday camps arranged by Stadt Zurich for local children. We picked the least adventurous activity (dance) as I figured rock climbing, kayaking and the like could be chancey without having enough German to know whether or not you were being told to release or lock the D-clip.
The kids really enjoyed the activities and loved the young camp leaders, who were excellent about including them with some English, as well as pushing them to learn some German, and being there for advice and assistance.
They got on well with some kids (though no enduring friendships) and weren't wild about some of the others, though this wasn't too much of an issue for them.
It was good value considering it was a two-week sleepaway. There were subsidies for lower incomes. At the time I booked (less than 4 weeks till start date) there were still plenty of vacancies at lots of the camp options.
So all in all, a reasonable supervised getaway for primary aged kids with some German, or those going with a friend or sibling.
Thanks all for your help.