Prefigurements from the Old Testament
Aineo do you sink your eyes into the Old Testament? If you don't, you should. And if you do, you should reread it. In order to better understand the New Testament, one must know the Old Testament.
There are many parallels in the Old & New Testaments. One of those is baptism.
First, baptism is done with water as it is in the Old Testament, not as baptism as we know it today though. I posted another reply that had to do with being "born again," go check it out; it's explained there more clearly.
Second, circumcision prefigures baptism. The ones who were circumcised were infants. In the New Testament the laws were not abolished but they were fulfilled and made perfect in the eyes of God. Just like the new Adam is Jesus, the new covenant or Sacrament, which was circumcision in the Old, became baptism in the New Testament so that ALL can be "born again" and have that covenant with God so that ALL can become children of God.
As far as the "households," I am not going to argue with you. There are other verses in the bible that also talk about "whole households" being baptized. There were people of all ages in each household. What makes you think that there WASN'T any infants in ANY of the households? Think about it. But most importantly, circumcision done to infants, prefigured the new covenant or Sacrament as we know it today as Baptism.