Trump can instruct the Justice Department to focus their law enforcement agencies on going after paedophiles but that is all he can do on his own. But for the most part sexual child abuse is not a federal crime, which it should be, it is only a federal crime if you use the internet, phone or mail to entice a minor to engage in sexual abuse, or if you transport a minor across state lines to sexually abuse a child, or if you transmit images or depictions of the abuse through the internet, phone or mail, or if the abuse takes place on federally owned land or property. The closest law that deals with child abuse on the federal level are 42USC 5106g which just defines abuse when it comes to a parent or caregiver either giving treatment or withholding treatment of a child medical condition that causes death or injury, but that also requires the states to enact the laws to enforce those definitions.