or by trusting in Christ?
Neither. When babies are baptized (as the Church has done from the earliest times), their sins are forgiven even though they neither "trust" in Christ nor "follow" the Law. God chose to redeem Mary at conception not because of anything she did. If you read any of the Pauline epistles you see grace as unmerited favor, God often picks people not because of merit. Think of St. Paul (aka Saul) himself. God's act of revealing himself to Saul was not based on Saul's following the Law or trusting in Christ. It was on account of God's good favor, not Saul's merit.
-A8
If baptizing babies has been done from the earliest times in the Church, give me book, chapter, and verse where I can read about it.
I may need to go baptize my son;)
Got ANYTHING (other than 'reasoning') to back up this assertion?
At least with Saul, there was a VOICE from Heaven speaking, and it is recorded as such.