These are small, resistant eukaryotes. They can survive drought, cold, lack of oxygen and even high radiation due to different cellular mechanisms and resting stages, which makes them very interesting for science. They got their name because they look like tiny bears.
Explanation for children:
Water bears are small eukaryotes that look a bit like a bear. They are especially interesting because they are very resistant, simply tough like a bear. They can survive drought, cold, lack of oxygen and even high radiation. You could even shoot them into space and it wouldn't harm them too much.