[MENTION=62]tango[/MENTION]
At the risk of upsetting people and driving this discussion into a ditch, the presence or lack of a satisfactory answer depends on what you think saves people. As one of those “mean Calvinists”, I have no problems with dead infants and salvation. If the infant lived to 20 years old, they would still be no more capable of saving themself than the newborn is (or than a 30 week old fetus is).
[Ephesians 2:1-5 NIV] 1 As for you, you were dead in your transgressions and sins, 2 in which you used to live when you followed the ways of this world and of the ruler of the kingdom of the air, the spirit who is now at work in those who are disobedient. 3 All of us also lived among them at one time, gratifying the cravings of our flesh and following its desires and thoughts. Like the rest, we were by nature deserving of wrath. 4 But because of his great love for us, God, who is rich in mercy, 5 made us alive with Christ even when we were dead in transgressions--it is by grace you have been saved.
This applies to anyone of any age.
[Romans 9:15-16 NIV] 15 For he says to Moses, "I will have mercy on whom I have mercy, and I will have compassion on whom I have compassion." 16 It does not, therefore, depend on human desire or effort, but on God's mercy.
This applies to anyone of any age, too.
So the infant is saved the same way that the teenager is and the same way that an adult is.
By the will of God and not the will of man.