It was sin, period. By attempting to make some distinction between what is curiosity and deviance is making a rationalization. Sin cannot be rationalized. Sin is sin, period. It makes NO DIFFERENCE whether it was 'curiosity' or deviance. It's sin.
All sin is deviance of some sort or other.
In the case of pedophiles the mantra should be ‘trust but verify’.
All this does explain why the girls started sleeping in their own room though. More difficult for the perp to do his thing and greater risk of being caught.