Do Mormons believe that babies need to be baptized?
Nope. We believe that that practice is wrong. Plain wrong.
The reason? Babies can't sin. What is baptism for? From lds.org, the Church's web site, it says, "Those who are baptized enter into a covenant with God to take upon themselves the name of Jesus Christ, keep His commandments, and serve Him to the end."
Through modern revelation we know that the Lord said, "They cannot sin, for power is not given unto Satan to tempt little children, until they begin to become accountable before me" (see D&C 29:46–47). They are not to be baptized until they reach the age of accountability, which the Lord has revealed to be eight years of age (see D&C 68:27). Anyone who claims that little children need baptism "denieth the mercies of Christ, and setteth at naught the atonement of him and the power of his redemption"
So, to summarize. Babies can't sin. Satan can't tempt them.
In fact, no one can sin until they are able to make a decision to do wrong. We believe that the age of accountability to be eight years old. That is when we baptize.
So, what happens if you are over eight and want to be baptized? It's okay. We can baptize anyone from age eight on up.
Just to follow up. What happens to babies who die and children under age eight who die?
We believe that they return to God and are with him. We have a chance to live with those children again if we keep the commandments.
Pretty cool huh? God provides for all his children.
It's true. You can find out too!