The Mainau Declaration is a special promise that some very important people made to take care of our planet Earth. They promise to do things to keep our planet healthy and make sure it will be a nice place to live for many years.
The people who made this promise are called scientists, and they are very smart because they study how the world works. They got together on a place called Mainau Island, which is a really pretty place with lots of flowers and trees.
The scientists talked about how important it is to take care of the Earth because we depend on it for our food, water, and shelter. They promised to do a lot of things to make sure the Earth is not hurt, like using less energy and reducing the amount of pollution in the air and water. They also talked about how everyone can help take care of the Earth by doing small things every day, like recycling and planting trees.
In the end, the scientists wrote this promise down on a special piece of paper called the Mainau Declaration, and signed it to show they are serious about keeping their promise. Now, people all around the world know about the Mainau Declaration and are doing their part to take care of the Earth too!