There's also the commitment from the godparents to raise the child in the faith.If a child dies below the age of accountability he will go to heaven BUT here's what you're not grasping. Once that child gets older, there is no guarantee he or she is going to be a believer and follower of Christ, so that child that you are claiming is "in the family" is actually NOT in the family forever until he or she makes the decision himself!
Sprinkling water on a baby has nothing to do with salvation, and again, a baby cannot make that decision, and you can't make that decision for someone else.