A method of treating a pediatric cancer in a subject in need thereof. The method includes administering to the subject a therapeutically effective amount of (S)—N-(5-((R)-2-(2,5-difluorophenyl)pyrrolidin-1-yl)-pyrazolo[1,5-a]pyrimidin-3-yl)-3-hydroxypyrrolidine-1-carboxamide, or a pharmaceutically acceptable salt thereof, or a combination thereof.