What's the difference between a baby christian..?

There no such thing as any of those...babies are incapable of understanding spiritual beliefs, much less deciding that they accept those beliefs. One isn't a member of any particular religion (or an atheist) until one has decided for himself or herself that she accepts the beliefs of that religion (and rejects the beliefs of the others).

Yes, there is an argument to be made that we're all 'atheist at birth' because we lack any kind of religious belief, though personally this is just semantics to me. In my view, you're an atheist when you've gone through the intellectual exercise and made the conscious choice to reject mythical, religious belief.

Baby Catholics get water poured over their heads at a ceremony.

The term 'baby Christian' does not refer to the young child of christian parents but actually refers to someone newly converted to Christianity who still does not understand all they need to know and still needs a little help and nurturing. All the others DO refer to the infant offspring of those you mention.

Christians are not born as Christians, they are born as human beings who become Christians once they understand the awesome love of Jesus Christ and accept Him as Lord and Saviour.

There is no difference. They are all unlucky enough to be born into an identity shoved down their throats by those who are supposed to be raising them into the ultimate form, regardless of whether that identity is for or against a deity.

There's no such thing. As a baby none of them will have any idea about religions and won't fully decide on what they are until much much later in life.

They are all the same - except at some point they will send the world into bankruptcy, hate and depression over a pathetic war.

All of the above are fictional, as babies don't know about gods hence don't have an active stance on them. You could say all babies are passive atheists.

absolutely nothing ! they are all innocent until they get old enough to know the difference between right & wrong, by then their minds are already being trained as to what they should believe in and which faith they should follow.

Nothing. But a Christian baby is sanctified if its parents are living godly lives.

The baby evolutionist finds a fish and says I wuv you grandpappy