His eyes would never open to see the wonders and sorrows of this world, but we are sure that they have opened to see the beauty and glory of Jesus Christ, of a perfect world of love that his family on earth have only begun to poorly imitate.
We shall lay his earthly remains in the grave, but not our hopes with them. Christ is risen, death is conquered, our night of weeping will give way to everlasting days of joy.
We live by promises, not explanations. George Whitefield wrote after the death of his second child "To explain God's providence by his promise, and not his promise by his providence, I find is the only way both to get and to keep our comforts." And his comforts come by speaking of his gospel promises that are stronger than death (1 Thess. 4:18).
Here is Article 17 of the Canons of Dort (1618)
The Salvation of the Infants of Believers
Since we must make judgments about God's will from his Word, which testifies that the children of believers are holy, not by nature but by virtue of the gracious covenant in which they together with their parents are included, godly parents ought not to doubt the election and salvation of their children whom God calls out of this life in infancy.