When Mormon (who abridged The Book of Mormon) asked the Lord about it, this was God's reply:
"Listen to the words of Christ, your Redeemer, your Lord and your God. Behold, I came into the world not to call the righteous but sinners to repentance; the whole need no physician, but they that are sick; wherefore, little children are whole, for they are not capable of committing sin; wherefore the curse of Adam is taken from them in me, that it hath no power over them...In N. Eldon Tanner's article, "To Those Searching for Happiness," he stated that the doctrine of infant baptism "was not part of Christ's original church," indeed, "no trace of such [was found] until the Third Century" (Ensign, May 1979, 14).
"But little children are alive in Christ, even from the foundation of the world; if not so, God is a partial God, and also a changeable God, and a respecter to persons; for how many little children have died without baptism!
"Wherefore, if little children could not be saved without baptism, these must have gone to an endless hell.
"Behold I say unto you, that he that supposeth that little children need baptism is in the gall of bitterness and in the bonds of iniquity; for he hath neither faith, hope, nor charity; wherefore, should he be cut off while in the thought, he must go down to hell.
"For awful is the wickedness to suppose that God saveth one child because of baptism, and the other must perish because he hath no baptism"(Moroni 8:8,12-15).
All little children are automatically saved by Christ's Atonement. Infants and children who die go strait to heaven to be with God in the Celestial Kingdom. Continue learning about baptism, including why we should be baptized, who should be baptized, and how we should be baptized.