It became that over time, after the beginning. Sure even now a whole family can be baptized at once, but the decisions are still individual. They just decided to be baptized together.
That calls for giving them peace through accurate education of the scriptures, not capitulating and reinforcing a false narrative.
No, baptism a la Mark 16:16 and Acts 2:38 solves it. After they have sinned is when forgiveness/salvation is relevant.
Oh yeah, original sin, also not in the Bible.
That family in Acts 16 was also spoken to in the middle of the night by Paul and Islas before getting baptized. Are you saying if they had babies, the parents woke them up, took them out, and had them listen to Paul and Islas before getting baptize. So sure, you could fail to see what the problem is with just about anything, if you make a casual glance and not look at it too closely.