We visited Hubby's colleague (who's also French and who like us has 3 kids) in Reutlingen before the end of Summer. He had this good idea of bringing us to Schloss Lichtenstein where there was this amazing tree-top walk in the forest (www.abenteuerpark-schlosslichtenstein.de) that the 2 men and our combined 3 boys (the women we ended up stuck with 3 other children on the ground) did.
The park's open from June to November and has 5 itineraries (easy to difficult). It takes about 2 hours to complete 2-3 itineraries. It costs 12 Euros for children between 8 and 15, 15 Euros for teenagers from 15 to 18 and 17 Euros for adults.
Could be an interesting Birthday Party venue when the kids are older (14 onwards) as the younger ones would need supervision in the order of 2 kids to one adult.
My eldest completed his course. At one stage I thought that he was going to give up as he was stuck and afraid, but peer pressure (from the other 2 older kids) gave him the courage to continue and once he gained confidence, everything became easier. Another reason to be pleased with this outing and to feel better about spending 2 hours waiting in the cold running after 2 babies.