Hello, this is Dr. E. Greetings from New York! I'm so glad you posted your question for me to answer, and I aim to provide you with accurate info.
There are studies that show that Vitamin E actually increases risk of death from a cardiac disease - no studies have been done on children. I would recommend stopping the Vitamin E - it is not proven to work and may actually make your child sick.
PS Osgood disease usually improves after stopping the activity that caused the fractures.