Playing by ear here means working out a tune once they can hear it or hold it in their inner ear, probably with guidance from you or an online tutorial, and does not exclude having some written instructions as back-up.
I would greatly appreciate your responses. I now have an orchestra of 70 in my one day a week job and I need to teach them more independence.
I would also be fascinated to hear how children who can play by ear learnt to do so...