The three things you note require only one consenting adult. However, I will reason like a judge here and rule for the perp.
Necrophilia is exempt from the consenting adults because one of them is dead, and it insults the court to even consider that a dead person can give consent. Therefore, as long as there is one consenting adult in this case, and as long as it is private, it is constitutional, and the police are not to interfere because it may harm the dignity of the live adult.
Animals are not listed in the Constitution. Therefore, animals are legal property of their owners. An animal is by logical definition, not an adult. Therefore, as long as bestiality takes place in the privacy of a home, and there is one consenting adult, it is constitutional, and the police are not to interfere because it may harm the dignity of the human adult.
Pedophilia deals with sex with children. Children are by definition not adults. However, if in the opinion of an adult, sex with a child would be beneficial to the child, and as long as it is in the privacy of the home, it is constitutional, and the police may not interfere because it would harm the dignity of the adult.
The Libertarian Party platform supports allowing children to declare their adulthood.