A convention for direction
Scientists agree to use a convention which shows the direction of the electric charge flow (the current) in a circuit as being from the positive terminal of the battery towards the negative terminal. This is in the opposite direction to the actual flow of electrons – the most common moving charges in circuits.
This odd state of affairs came about because the convention was established before it was known that electrons move through the wires of a circuit.
However, the current direction convention is not important for understanding electric circuits and we'd suggest not making a big fuss about it in the discussions you have with children.