Insist… and gain
voltage is more approachable than the phrase
potential difference so is probably enough for 11–14 year old children. A more sophisticated development that justifies the term
potential difference is probably not appropriate for a class of 11–14 year-olds. Voltage drops and gains, later referred to as potential drops and rises, by analogy with gravitational potential difference, might also best be excised from the classroom for now. Indeed, the whole idea of potential difference is one that is hard for post-16 students. We'd suggest leaving the hills analogy to then. There may be a case for introducing it subtly in 14–16 teaching. But you should beware of the difficulties, as the
electrical hills are only there when there is a loop with current in the circuit elements. It's not much like a circular route in the fells, where the hills are there, whether or not there is a flow of walkers along the path. You always need to take care not to lead pupils off along the wrong tracks by injecting a half-developed analogy.
Relating voltage to power, as what is happening
now in the circuit, may be a more profitable approach. Introduce it as the second factor that determines the brightness of a bulb: you'll need to specify both the voltage and the current.