When a battery is connected to a bulb to make a complete circuit, the bulb lights up. If you are interested in understanding how electric circuits work, this familiar event raises a number of questions.
While the bulb is
lit the battery is
flattened and the filament of the bulb glows and light is emitted (see the SPT: Energy topic and the SPT: Electric circuits topic for more detail).
The bulb lights up very quickly as the circuit is completed. The situation flips from one steady state, where there is very little happening, to a steady state, where the bulb is glowing, very quickly. We're going to suggest that you concentrate on the steady state, where the bulb is glowing steadily.
What's needed is a way of thinking about electric circuits that allows you to reason about what's going on inside them (inside the battery, wires and bulb). You can see the effect of what's going on (the bulb lighting up); what is needed is a model for the electric circuit to support you as you help children who want to explore this process.
Most of this Physics Narrative is for your benefit, and there is just too much there for primary-aged children.