Let me tell you a story. There was once an atheist family. A mother, father and daughter. Their house burned down one night, and both parents died, but the little girl survived. And she was adopted to a christian family. They took her to sunday school, and the teacher told her about Jesus, and showed her a picture. Then the girl said: "I know that man.." The others didnt understand anything. She had never heard about Jesus ever in her life. she countinued "He's the one who held my hand the night my parents died..."
I think Jesus has a special relation to all children. That is why He speaks so well about them in the Bible. But we must not forget the fact that also children can reject Jesus, no matter what age they are in. We dont want to think that anyone will come to hell. especially little children. But the fact is that all children are sinners, just like the rest, and we cannot say that they have a free pass to heaven because they are children. God loves them, but they are still sinners. And they have to except Jesus to enter.
Now that doesnt mean that they have to except Him in the way we might think. But in one way or another.. They have to make a choice, just like the rest. no one is born doomed, or with a free pass to heaven.. (sorry if you are offended, I know its hard to think that little children can go to hell..)
God bless!