I think you just have to decide what your own child is personally capable of processing. DD who just turned 10 watched Matilda when she was 5 and every year after, and loved it. She watched A Wrinkle In Time when she was 8 and we still watch it periodically and she loves it. At 9, she watched all 8 Harry Potter movies twice and loved them. However, at 9, we tried to watch Life of Pi and she was overwhelmed with emotion and we had to turn that off fairly quickly.