My kids (5&8) would like to enter a summer school to brush up their Swiss- German to be able to communicate with their Grandfather better. Ideally it should be located somewhere around the city of Baden/AG.
Any help?

Not sure if you really want a summer school if you want them to study swiss german. Perhaps a camp or language school would be more appropriate. And summer school for a 5 year old, not sure if that would exist at all here anyhow.

Thanks, a playgroup or a camp for 2 week would be ok. I was looking for a bit exposure to meet other kids too.

Do your kids speak any German? The Canton offers summer camps, but I think residency is a requirement. Here are some links (sorry only in German).

http://www.jugendsportcamp.ch/

WWF offers summer camps. Here is the link to the programme.
http://www.wwf.ch/de/derwwf/jugend/kinder/ferienlager/

Many thanks for that. It looks like that we have to wait for another 2-3 years before we can enroll them, but it is certainly a great option.
Most appreciated

I bet they don't. I bet they really want to spend their holiday playing and splashing, slurping icecreams and running round with other kids, having pure fun!!

This is what I was going to say. If they've asked for this they're the only young kids in the world who would...

Actually, the best way to learn to communicate with Gran'dad is to leave him and the kids together. don't hover, just leave them to it. They will find a way to understand each other.