I don't know what Universalism is, but I don't believe that we are under "Original Sin" beyond the fact that we find ourselves still outside of Eden. There was a separation that happened between man and God at that time and I figure we don't totally overcome that until we die or Jesus comes. But we are clearly not condemned to Hell because our earthly fathers sinned. And a baby cannot sin as he/she is incapable of knowing the difference between good and evil. Baptizing babies is a pointless practice and quite frankly is impossible because believing, repenting, and confessing are not possible at that stage in life. I watched a five year old girl at her mother's funeral and she was totally oblivious to what had happened. I don't think she was old enough to understand salvation. For each person it is different. But babies, never.
Hmm something caught my eye -
Do people think that when we say the sin nature inherited by Adam, we equate it to the sins of the father?
No - we inherit the sin nature - bent towards sin, slave to sin etc
Is a child innocent of his father's sin - yes
Can a child be brought up with the example of sin, and thus reproduce that kind of sin, yes
Is God just to do whatever He wills with His creation - yes