One represents a cultured aspect of American culture, the other is a horrifying invention that MIGHT (currently unproven) serve as a crime deterrent.
Adult sex dolls are art, they are beautiful invention. They represent the beautiful form of humans and are the means of simulation the spark of creation of the human body. Adult sex dolls ought to be protected art, just like any other statue. To engage with an adult sex doll is to engage in culture, fulfilment, and enjoyment.
Child sex dolls are to simulate extreme child abuse by the depraved unfortunates. There maybe a utility for them, which is the hypothesis (unproven) that they prevent rapes of real children. Child sex dolls represent a horrific aspect of the human psyche, and ought to be kept behind close doors and those who engage in such objects ought to be ashamed.