Best way of explaining is using the gold analogy.
But I think explaining it to a person in his/her early teens will be quite diffiicult. Best to wait till the person reaches late teens and then explain
Bitcoin is not easy to explaine and cant blame people not to believed you with one sitting of explaination.In teens maybe 70-80% chances that they will understand but its still depend on them if they will accept your explaination.In children maybe just let them play Im 100% sure they are not intersted in bitcoin.