If you read Matthew 18 : 6 and 14 you will know that the little ones among us need to have faith in order to be saved and that they could also be lost. I believe there is not one being in the entire mankind who doesn’t need our Lord Jesus to save him from being condemned, even the little ones need salvation otherwise they could be lost. Moreover read also Psalms 51 : 5 to see that you become a sinner since the time you are conceived in your mother’s womb.
I never said that little children don’t sin. As you pointed out by citing Psalm 51:5 a sinful life is the destiny of every human being. What I am saying is that God doesn’t count the sins of children against them until they become old enough to understand the difference between right and wrong.
The clearest explanation of this is in Romans 7:9 where Paul said, “Once I was alive apart from the law, but when the commandment came sin sprang to life and I died.” Obviously he was talking about spiritual, not physical, death. As a child he had eternal life because he wasn’t responsible for his behavior. When he reached the age of accountability he became subject to the commandments, and at that moment he became a sinner in God’s eyes, destined for death.
In Matt. 18:6 the person being condemned is not the “little one” who sins but the adult who causes it. The phrase “little one” refers to the little child Jesus was pointing to in verse 5. In verse 14 when He says the Father is not willing that any of these little ones be lost, He doesn’t mean that it could happen. He means He won’t let it happen.
Your opinion that children can be condemned for their sins, even though they’re not intellectually mature enough to understand the spiritual consequences of their behavior is not compatible with the character of God, nor is it consistent with what the Bible teaches.