Dr. Mohler and Dr. Daniel Akin have reposted their article showing from scripture why they believe that infants go to heaven when they die.
they lay out six reasons for this belief. here is number six and an overall point about God’s justice, but do go read the whole thing. Including Charles Spurgeon in the conclusion
Sixth, some in Scripture are said to be chosen or sanctified from the womb (1 Samuel 1:8-2:21; Jeremiah 1:5; Luke 1:15). This certainly affirms the salvation of some infants and repudiates the view that only baptized babies are assured of heaven. Neither Samuel, Jeremiah or John the Baptist was baptized.
After surveying these arguments, it is important for us to remember that anyone who is saved is saved because of the grace of God, the saving work of Jesus Christ and the undeserved and unmerited regenerating work of the Holy Spirit. Like all who have ever lived, except for Jesus, infants need to be saved. Only Jesus can take away their sin, and if they are saved it is because of His sovereign grace and abounding mercy. Abraham said, “Will not the Judge of all the earth do right?” (Genesis 18:25). We can confidently say, “Yes, He will.” When it comes to those incapable of volitional, willful acts of sin, we can rest assured God will, indeed, do right. Precious little ones are the objects of His saving mercy and grace.