We left alone but it was on the ball of DD's foot and eventually started to affect her walking - she started walking on the side of her foot.
So I used the paint-on stuff which was a waste of time and eventually decided it was time to utilise the services of our doctor, whom we never see. It took five freezing treatments over a period of 4-5 months iirc to get to a stage where it looked like it might disappear. Then we went on a seaside holiday and, as a number of friends had predicted, it disappeared thanks to the constant rubbing of the sand as she ran around the beach.