During heavy rain, this is where the pond will drain. You may want to put gravel and rocks along the course that the run-off water will take. If it takes a route that is disruptive to your garden beds, dig a small channel to guide the water in another direction. Finally, populate your pond. Because the pond is so small and does not have circulating water, it will be difficult to maintain a balanced system.
Tadpoles are adaptable and can survive less stable ponds.
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.