The Catechism in Questions & Answers

489. Why can children be baptised?

The statement of Jesus: “Let the little children come to Me, and do not forbid them; for of such is the kingdom of God” (Mark 10: 14) indicates that the blessings of God should also be made accessible to children. This includes the sacraments.
The New Testament attests that entire households were baptised together: “And immediately he and all his family were baptised...” (Acts 16: 33; cf. also 16: 15). Households and families include children. From this the Christian tradition of baptising children has developed.
Moreover, when children are baptised, those entitled to raise them profess belief in Jesus Christ on their behalf and take responsibility for the religious education of their children in the sense of the gospel.

“Then Crispus, the ruler of the synagogue, believed on the Lord with all his household. And many of the Corinthians, hearing, believed and were baptised.”
Acts 18: 8