You should take a look at Processing 3 (a graphical Java). My dad introduced me to it at about 12yrs. All he did was give me a YouTube playlist to work through and it has held my interest till this day.

I would say any framework with a narrow focus on graphics and instant graphical feedback (like SFML for C++) would be great for kids or any beginner. Also, Khan Academy has great resources based on ProcessingJS and even a simple submission board with a community of other young learners.