We also know that, in the New Testament, circumcision continued to be a sign of a true evangelical relationship to God (Rom. 2:29). Christian Jews continued to apply that sign to their infants (Acts 21:21). Such circumcision meant that such children were members of their parents’ synagogue, and we know believing Jews assembled in Christian synagogues (Jas. 2:2). These were also considered Christian churches (Jas. 5:14). Therefore we know that certain first-century churches had infant members.
Wilson succinctly summarizes a whole chapter here, and it is a little pondered/discussed, but very convincing, argument when taken seriously.
