The Heidelberg Catechism

Are infants also to be baptized?

Yes: for since they, as well as the adult, are included in the covenant and church of God; [215] and since redemption from sin [216] by the blood of Christ, and the Holy Ghost, the author of faith, is promised to them no less than to the adult; [217] they must therefore by baptism, as a sign of the covenant, be also admitted into the christian church; and be distinguished from the children of unbelievers [218] as was done in the old covenant or testament by circumcision, [219] instead of which baptism is instituted [220] in the new covenant.