Ok Kerrymum, have been thinking about your post.
Things I would look for in a child who was gifted at music - the main thing is that it seems to be 'part' of them - this sounds quite 'la-di-dah' but what I mean is that they can't help but make music. They will take every opportunity to play, listen, sing, make music with others. You can't imagine the child without music. They don't struggle over learning a piece, and they will enjoy the challenge of learning a hard piece. They will do their lesson pieces, but will play for fun for hours besides their regular practice.
Playing music will seem easy - in watching them the listener will think 'it's not so hard really', however hard the piece, because it is done with a sense of ease. The music they play 'speaks' to the listener in some way - it is not just notes, but something deeper that touches the listener inside.
Does that make any sense? I'll keep thinking - it's one of those things that is hideously difficult to define, but it made me think a bit more of what I think 'gifted' is in a wider sense. I think the difference between a 'clever' child and a 'gifted' child is the 'need' to learn. A clever child can learn everything they're given and understand, a 'gifted' one has a physical NEED to learn more about the world and things.