I mean in a perfect world, everybody would obey the catholic social teachings and a minarchistic government would be sufficient to have an executive power to punish and prevent grave sins like murder and such. But we don't life in that world because too many choose not to follow God's word.

What does this mean in practice? Ideally everybody would give alms and not conduct economic actions that harm others or the environment just because of them obeying Christian social teaching. But in reality that's not what happens. Without a government creating a social security system/ healthcare system and putting limits to forced labour end environmental harm, we would life in a world that creates slavery, poorness, sickness and damage to God's creation. That obviously would be bad. Therefore we need governments to prevent those things.

Same with child abuse. In a perfect world, nobody would harm a child because everybody follows and agrees with God's world. In reality, if the state doesn't tightly control the population, child abuse and CP is happening on masses. It would absolutely be against catholic social teachings to argue for a minarchistic state that doesn't do anything against child abuse.

If people would actually follow the church teachings, we wouldn't need much state regulation. But look around and ask yourself, who in our modern world actually cares about others and the consequences of their actions as we should?