"But now he is dead. Why should I fast? Can I bring him back again? I shall go to him, but he will not return to me.”
-David, 2 Sam. 12:23(ESV)
I often see this verse interpreted as David referring to his son as being in heaven. Now I'm not saying his son did not go to heaven, but all David is saying here is that he too will die and be in Sheol.
What you state isn't Scripture taken out of context, In my humble opinion. In fact, historically it's been the common understanding of this passage by Calvinist and Reformed Bible commentators. See as follows some examples of this point.
Matthew Poole states:
"
I shall go to him; into the state of the dead, in which he is, and into heaven, where I doubt not I shall find him."
Matthew Henry states:
"
I shall go to him. First, To him to the grave. Note, The consideration of our own death should moderate our sorrow at the death of our relations. It is the common lot; instead of mourning for their death, we should think of our own: and, whatever loss we have of them now, we shall die shortly, and go to them.
Secondly, To him to heaven, to a state of blessedness, which even the Old Testament saints had some expectation of. Godly parents have great reason to hope concerning their children that die in infancy that it is well with their souls in the other world; for
the promise is to us and to our seed, which shall be performed to those that do not put a bar in their own door, as infants do not.
Favores sunt ampliandi - Favours received should produce the hope of more. God calls those his children that are born unto him; and, if they be his, he will save them. This may comfort us when our children are removed from us by death, they are better provided for, both in work and wealth, than they could have been in this world. We shall be with them shortly, to part no more."
John Gill states:
"
I shall go to him; to the state of the dead, to the grave, where his body was, or would be; to heaven and eternal happiness, where his soul was, as he comfortably hoped and believed: from whence it appears, that the Old Testament saints did not suppose an annihilation at death; but believed the immortality of the soul, a future state after death of eternal life and bliss:"
1599 Geneva Bible notes:
"2 Sam. 12:23 - But now he is dead, wherefore should I fast?
(n) can I bring him back again? I shall go to him, but he shall not return to me.
(n) By this consideration he appeased his sorrow."