Pupils need to be old enough to read, to say the alphabet backwards from G, and to play five consecutive piano keys with a hint of independence of finger movement. It's essential that very young pupils love stories, since Musicland abounds with them...
Children under the age of six are probably a bit too young. You cannot, however, be too old, and this includes those starting from scratch.
While real pianos are better than digital ones, a reasonable digital piano with weighted keys will do (and I'm happy to give advice on renting or buying a piano. It's a big decision). Sometimes, in a busy household, using headphones is unavoidable. But it's best to play out loud as a general rule. You also need an adjustable stool or an improvised equivalent. Children whose feet do not yet reach the ground need to rest their feet on something. A pile of books or a small box will do.
Parents of young children
Parents are welcome to wait in the (comfortable!) kitchen, and have a cup of tea. From here, they can hear everything that’s going on in the lesson. We often ask parents to join us when there is something particularly interesting that we want to show them or, at the end of the lesson, to summarise what we covered.
Parents have a vital role to play in the learning of music at home, of course. Practice notebooks are as much for parents as they are for their children, so that they can go over the practicing requirements for that week and listen, help and praise. Having music on at home (particularly by the composers of the pieces their children are learning) is invaluable, as is taking children to concerts and musical outreach events. Britten Sinfonia and the Cambridge Faculty of Music Outreach Department, for example, do great events for families and young people.
Above all, parents are the most important, forbearing and appreciative concert audiences ever (with the possible exception of grandparents).
Picture: Phantom Hands at the piano by Bruce Guenter, Flickr