The plants mentioned above, duckweed and cabbage plant, will also do well. Bear in mind that the pond will require ongoing care and maintenance, including emptying, cleaning and refilling. Working to maintain it as a living system is an exciting longterm project that some children in the group may want to take on. Sun is also necessary for water plants to grow. Algae produce oxygen but also fill the pond with organic material as they die.
Water plants add oxygen to the water.
They need oxygen in order to survive. They produce carbon dioxide gas, which the underwater plants need in order to live.