For the promise is unto you, and to your children, and to all that are afar off, even as many as the LORD our God shall call. And she constrained us. Necessity of baptism for all, including children. For as by one man's disobedience many were made sinners, so by the obedience of one shall many be made righteous. Buried with him in baptism, wherein also ye are risen with him through the faith of the operation of God, who hath raised him from the dead.
Children can be believers.
And whosoever shall offend one of these little ones that believe in me , it is better for him that a millstone were hanged about his neck, and he were cast into the sea. For, lo, as soon as the voice of thy salutation sounded in mine ears, the babe leaped in my womb for joy .