“how did infant baptism become a thing”?
Well, you read in the book of acts of “entire households” being baptised, not “all the adults in the household” but “ENTIRE households”
inscriptions dating back to the 2nd century which refer to young children being baptised - Corpus Inscriptionum Graecarum, 9727, 9801, 9817; E. Diehl, Inscriptiones Latinae Christianae Veteres (Berlin 1961), nos. 1523(3), 4429A.
The earliest reference to infant baptism was by Irenaeus (c. 130–202) in his work Against Heresies in AD 180 —
infants, and children, and youths, and old men. Therefore he passed through every age, becoming an infant for infants, sanctifying infants; a child for children, sanctifying those who are of that age . . . [so that] he might be the perfect teacher in all things, perfect not only in respect to the setting forth of truth, perfect also in respect to relative age” (Against Heresies 2:22:4 [A.D. 189]).
Augustine wrote of the universal custom of baptizing infants around 300 AD
While Tertullian writing c. 198–203 advises the postponement of baptism of little children and the unmarried, he mentions that it was customary to baptise infants, with sponsors speaking on their behalf.
So it is definite that infants were baptised at least from Apostolic times
Then logically - by extension - shouldn't infants take communion, too?