Child psychology question?

I have 2 nephews aged 4 and 6. Both have hijacked my comic book collection and I have no problems with that. These guys like my mickey mouse, donald duck, daffy duck books quite a lot. They also like Superman, Batman, Spiderman. They also like the amar chitra kathas- especially they seem to like all the rakshasas and Hanuman. Of late I noticed they have taken extra interest in the comic books featuring Wonder woman, Batgirl, Catwoman. Earlier this used to be both of them looking at the pictures and giggling naughtily at the amount of skin or the curves. Of late I find these cartoon girls have been descrated. These guys have been amplifying the physical attributes beyond the point of elegance intended by the original artists using their crayons. My threat of doing the same to Mickey Mouse has curbed the problem. Anyways their parents feel its nothing to worry about. Am sure the kids are very innocent. But should one take care of not exposing children to skin shows. Should one try to restrict what they see?