Oh, I'm aware of how it was established for the faithful... I was zeroing in on the baptism of infants. I guess I should have asked, How/when did God give the directive to baptize babies/children?
As it pertains to baptizing children, I'm assuming we are to read that 'household' covers them in the scriptures provided. It's not explicit as to whether the the households were baptized by choice, nor if it was 'required' of them through familial associations. Is there a piece of doctrine that supports the practice that you know of? In all of my Bible reading/studying, or other learning, I've never come across scriptural support (not that I've been looking for it).