To baptize the infant children of believing parents is a beautiful picture of the sovereign grace of God. Because with the coming of the New Covenant, all men had to enter by way of repentance and receive the New Covenant sign and seal. Since the concern of the New Testament is upon the progress of the gospel, it focuses upon the conversions to the faith rather than the internal workings of the Church. The gospel is being proclaimed to adults and thus, there must be repentance and faith before the sign of the covenant is given. The question is how were the children of these converts viewed and here there are numerous indications that they were considered covenant members as before under the Old Covenant.
Children are to be baptized.
We cannot know that. But we do know that God includes them in the covenant. We cannot presume that since we cannot see their hearts. Covenant baptism is not based upon presumption but the clear command of God to give the sign of His covenant to our children. If they don't, they will be covenant breakers and suffer the condemnation of old Israel.