Those considered to be in Church per the NT are those actually i in the body of Christ, placed in it by the Holy Spirit when faith was placed into the work and person of Christ..Phil,
Your post presupposes a command was needed. What was needed was not a command to baptize infants but rather a proper understanding that baptism was to be administered (once) to those who were to be considered part of the church.
Your point that household baptisms are inconclusive would seem to miss the point of corroborating evidence. When we come to the NT we should expect to see household baptism. We should also not expect to see a child from a covenant home undergo baptism after coming of age. Both expectations are met, as anticipated. They serve to corroborate covenant baptism.
Passages such as Ephesians 4 and when Paul stated that we have now been sealed in and by the promised Holy Spirit in the New Birth.