I think she means the child in question is unfortunately ignorant, rather than innocent. To me, innocence implies being untainted by the knowledge of evil, not spared from knowledge you need in order to do the good you’re capable of doing, which is what she’s implying is the problem.
A small child who has been spared from knowledge they are not mature enough to use yet is not culpable, but even though they are guilty of no sin, I don’t think I’d use the word innocent, because innocent is a good kind of unknowing.
Young children are capable of learning what they may not touch and when they cannot touch what they are allowed to touch at other times, including respecting the bodies of other people. I think this is what the OP meant. A child who is still breastfeeding can easily learn that he or she only has permission with his or her own mother, and that even that is not universal to every time and situation. It doesn’t require slapping, but it does require a willingness to train the child through firm and consistent correction.