"What God has joined, man must not divide." In the one marital act, God has joined two gifts: life and love. The life-giving and love-giving aspects of the marital act are separated by the anti-life will necessarily involved by every use of artificial contraception. This is why the Church absolutely excludes its use as a moral evil in each and every circumstance.
"Let the children come to me" in the sacredness of the gift whereby husband and wife truly become "one flesh" in the sacrament of marriage, where every marital act is open to new life.