Once again, just my 2 cents worth:
Psa 51:5 Behold, I was shapen in iniquity; and in sin did my mother conceive me.
We are born with a sin nature and this can be plainly demonstrated. I have yet to meet a baby or young child that needs to be taught to do wrong but they all need instruction in what is good and right.
Sweet yes, born sinless no. Until they reach the age of accountability they are certainly Christ's.
Scripture indicates that when man partook of the tree of the knowledge of good and evil that he could no longer stand in God's presence. Man was once led of God but now he was dependent on his own mind for direction- the carnal mind is always at enmity with God and even man's "good" is but a filthy rag.
These are just my views and I do of course respect your right to your own.