Thanks for the info, it helped a lot.
This is what we did:
Klangweg, www.klangwelt.ch/ch/index.php?open=klangweg a great way to experience hiking with kids. The walk is about 10 km, but the about 25 klang-stations "shortened" the walk.
Mainau, http://mainau.de/, beautiful flower island, that combines the kids need for play and adventure with the parents need for relaxation.
Ravensburg, http://www.ravensburger.de/spielelandL/ our kids, aged 4&7, loved it. But at 7 you're almost too old. Next time will go for Legoland. Went there on a sunday, great day to visit, not so many visitors.
Alpamare, http://www.alpamare.ch/, great waterland! Event though we went there at 6pm it was quite crowdy with sometimes long ques for the waterslides.
Chaserrugg, http://www.chaeserrugg.ch/de/sommer/home.html . The views are, as always in Switzerland, spectacular. However the slopes are steep and kids likes to go close to them.... Also very expensive for a family.
Again, lots of thanks for all the useful info.
Rgds
Krilon