The Dreaming Jewels aka The Synthetic Man by Theodore Sturgeon
The novel “The Dreaming Jewels”, also known as “The Synthetic Man”, by Theodore Sturgeon was published for the first time in 1950 in the magazine “Fantastic Adventures” and then as a book in a revised edition.
Horty is 8 years old when is caught eating ants. His strange behavior angers his adoptive father and as a result of the fight that follows, he loses three fingers on one hand. Horty decides that the best thing he can do is run away from home with only one jack-in-the-box he cares about very much. He literally jumps on the first passing truck, where he meets some people who work in a circus who invite him to go with them.
The circus owner Pierre Monetre isn’t very friendly but Zena, a dwarf who met Horty on the truck, convinces her boss to welcome the child by passing him off as a dwarf girl like her. Horty’s life seems to improve markedly in an environment where people generally love each other but Zena warns him not to tell anyone that the fingers he had lost have grown back.