One of the great debates in Christianity is the one regarding infant baptism. The simple fact is that the bible neither speaks of it explicitly or prohibit it. What we do know for a fact is that, as recorded in today's first reading, when men were moved by the preaching of the Apostle, the entire family would be baptized into the Church. Nothing in the scriptures suggests a minimum age below which one was excluded.
Both the Jewish and gentile cultures of the day saw the family as a single unit. This would have often included slaves as well as children, literally everyone in the household.
From a historical perspective one need only look at our Jewish roots and see that the infants too are considered part of the covenant. While some Christians like to point to the bar mitzvah ritual for coming of age, they forget that at the time of Jesus the Bar Mitzvah did not yet exist. What did exists was the circumcision on the eighth day.
From the modern perspective of human development, we now understand that those early months and years can impact a person for the rest of their life. It is only logical that we would want that gift of the Holy Spirit poured into the child as soon as possible.
If we truly believe that baptism is more than symbolic, that grace has real power, why would we delay in giving that gift to the next generation?