"The heart of man is deceitful above all things and desperately wicked"

"God is faithful to save everyone who sincerely comes to Him in childlike faith."

I am interested to know at which point you believe the heart of a child turns into one that is "deceitful above all things and desperately wicked"

"We were born marred by sin"

"God sees us all as rotten until we are made new through Jesus Christ"

Now, by that logic, any children that die before they even understand religion are doomed. Is that so?