MIT’s OCW is free and includes enough math to keep your friend’s kid busy for a long time. https://ocw.mit.edu/search/?d=Mathematics&s=department_course_number

MIT’s OCW is free and includes enough math to keep your friend’s kid busy for a long time. https://ocw.mit.edu/search/?d=Mathematics&s=department_course_numbers.sort_coursenum https://ocw.mit.edu/search/?d=Mathematics&s=department_cours...