and want to bring clean water and vegetables as souvenir for their parents after the summer camp.

From the tweets by @s_kiyoe, who set up a summer camp (in Shizuoka Prefecture, I think, judging by the town's name but I could be wrong) for children in Fukushima Prefecture. The original tweets are in Japanese:

Our fun-filled summer camp was finally over. We all cried at parting, because they didn't want to go back, and we didn't want them to go back to Fukushima under the current situation. Many Fukushima children were collecting empty plastic bottles. They said they wanted to fill the bottles with clean, safe water that they drank at the camp and bring them to their parents.

The bus arrived at the temple [where the camp was held] to take the children back to Fukushima. We asked them, "Where would you like to go to buy souvenirs?" They answered "Please take us where we can buy locally-grown vegetables, not supermarkets." Safe vegetables for their families.