This will sound funny - but the best thing to help is a baked potato! I kid you not. I read this years ago in Parents magazine and it works great!
You cook a baked potato in the microwave and then put the potato in a sock. Then the child can hold the nice warm 'sock' to thier ear. The great thing about it is that it stays warm for a really long time, it is soft and you can let them go to bed with it and not worry about electrical cords or a leaking hot water bottle.
Try it - you will not be sorry!