The Wonder-Child by Ethel Sybil Turner

A small girl of eight had, with incredible exertion, put the huge saddle on its back; Bartie had nothing to do but fasten the girths in place and put on the bridle. He flung himself up, and moved the animal close to a stump; Floss, the small girl, climbed to a place behind him, and a nine-year-old boy, playing marbles near, rose up at the sight of the moving horse, pocketed his marbles, swung his bag of books round his neck, and clambered up to the third place on the steed's broad neck.
All the paddock was a-move. There was a general race down to the sliprails, a gentle thunder of horses' hoofs and boys' shouts, broken by the shriller cries and 'Good-byes' of the girls.