I found out I think when I was 10. I heard it from someone else and asked my mom if it was true. She told me the truth and I cried. I selected 10-11 but I think 9-10 you should tell them. I think its better to hear from your parents then someone from school or something. I also think they should know around when most people would find out. Depends on with different kids though I think. For some reason I think I would tell a boy earlier then I would tell a girl...