Just explain to them how a motor takes much more current to start and get up to speed than to run at that speed. Have them think about how little fuel is required to hold 60MPH on the highway. It will be intuitive to them that it takes more when they go from zero to sixty. Then have them consider what it would take from under their hood if their car could even come close to zero to sixty in under three seconds. Then just explain that the huge current draw causes a voltage drop that causes the lights to dim even though they draw little current.
Joe
