If a mother and father with a female child walked into the store where I work and the child was wearing that t-shirt, and I said I thought the shirt was offensive and inappropriate attire for a child, my employer would fire me. We have a much bigger problem in this country than just the seller and Amazon.
Nothing stopping you from noting the name of the credit card and after a few weeks delay anonymously reporting a possible child sexual abuse case to the authorities.
Much bigger.