The quote you're referencing is from Jenny Kitzinger and is as follows:

"The twin concepts of innocence and ignorance are vehicles for adult double standards. A child is ignorant if she doesn't know what adults want her to know, but innocent if she doesn't know what adults don't want her to know."

It comes from the article "Who Are You Kidding? Children, Power and the Struggle against Sexual Abuse" which can be found in the book Constructing and Reconstructing Childhood ⚠️ ↗.