My 7 yr old dd is going through a stage of masturbating frequently. I've tried, as gently as possibly, to explain that whilst what she's doing is fine, normal, and lots of people do it, it's best done in private. However as soon as she's immersed in something, she seems to forget and starts again - and the final straw was her lovely teacher telling me that 'her hand was in her knickers all through assembly' 
Please tell me that some of you have been through similar?!!!