You need no licence for our boats
Pedal boats, kayaks and canoes are moved by muscle power, that is by pedalling or paddling. For muscle-powered boats like these there is generally no licence requirement in Germany. So you can simply come, rent a boat and set off.
You get a short briefing on site: how to get in and out, how to steer and what to watch for on the water. That's plenty, even if you've never been on a boat before.
When would a licence be needed at all?
In Germany a licence only becomes mandatory for motorboats above a certain power (15 hp, or 11.03 kW). Since our boats have no strong motor, that doesn't apply to you.
What to bring instead
Instead of a licence, common sense counts most: follow the briefing, don't overestimate yourself or the children, and keep an eye on the weather. If a thunderstorm approaches, always head back to shore in good time.