Rocking Horse Christmas by Mary Pope Osborne
One Christmas Morning, when a boy finds a rocking horse under the tree, he climbs on its back and they ride away on the world's most wonderous adventures. But then the boy grows up and the toy is increasingly forgotten-'til one-day the horse is re-claimed by the grown-up boy's son. As the School Library Journal notes "The theme of toys outgrown and put aside but not forgotten is so well done here that it will strike a chord with many children".