[annalex]

The first Chriastians were adult converts and indeed practiced the Catholic form of baptism for adults, which involved a profession of faith and penance and is similar to the valid forms of Protestant baptism of adults. Once they were converted, they had their entire household baptized:

15 And when she was baptized, and her household...

33 ... he ... was baptized, and all his house immediately. (Acts 16)

[Marysecretary]

Do Catholics immerse? They baptize infants. Immersion was usually used by the early Christians and probably mostly adults and children old enough to know what they were doing.