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 metal wires, so in most classroom circuits, and in many situations in the home as well.
This somewhat unhelpful state of affairs came about because the convention was established before it was known that electrons move through the wires of a circuit.
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. You can thihnk about something flowing and not worry to much about exactly what is flowing.