If you have maggots or tiny worms inside the peaches then it is too late to get rid of them now. They are most likely larvae from a fly that inserted eggs into the fruit as it was ripening. A barrier control such as fine netting to keep insects from landing on the fruit is the practical way to keep the flies from the fruit. Clean up around the base of the tree and remove the infected fruit to keep the maggots from spreading and overwintering in leaf litter.