Is it normal for 8 year old girls to masturbate?

It happens. If this is happening it suggests someone in her close circle introduced her to the process and that person may have been sexually exploited. I would approach it as a mater of fact rather than shaming. She can find more productive ways to use her time that do not place her private parts at risk for injury or infection. If she must, it must by like a potty break, alone & out of sight.

How would someone know when to start anything? Depending upon, person’s interest, they learn riding their bike, swimming, or playing piano. No one questioned Amadeus Mozart when he started playing his own compositions before age 6. Once a person discovers the pleasure of orgasm, craving persists. Read “Coma” by Michael Crichton. Explain the limit and make it safe. Hope it helps .