Here are my thoughts, and being that this is the book of Revelation, am basing these thoughts on clues provided in the Revelation 12 text. I could be wrong, but here is what it seems to me.
When I think about the manchild, I also think about the woman who births the child.
1And there appeared a great wonder in heaven; a woman clothed with the sun, and the moon under her feet, and upon her head a crown of twelve stars: 2And she being with child cried, travailing in birth, and pained to be delivered.
Clothed with the sun and wearing a crown of twelve stars. Christ had 12 disciples and I take the metaphor, "clothed with the sun," to be a metaphor similar to the white linen surrounded with Light, truth, virtue. It seems to me that this is a reference to the church, a gathering of people in Christ, in which every believer is birthed into the world, who the devil desires to sift, and devour.
3And there appeared another wonder in heaven; and behold a great red dragon, having seven heads and ten horns, and seven crowns upon his heads. 4And his tail drew the third part of the stars of heaven, and did cast them to the earth: and the dragon stood before the woman which was ready to be delivered, for to devour her child as soon as it was born.
It says in the next verses that the child is to "rule all nations" and that he is "caught up unto God and his thrown" promises that in other places in Revelation are given to "the overcomer," while the woman flees into the wilderness to be fed. One could interpret this as a separation of the woman and the manchild, but I don't believe so.
I believe what is happening is that while the church is in the earth beset and chased into the wilderness by the devil, the children of that woman are sitting on thrones as they are persecuted. In other words, I believe this is talking about how the persecuted church is in a higher place in their minds, sitting on the throne of God even while inhabiting this earth in which they are pilgrims.
11And they (the bretheren) overcame him by the blood of the Lamb, and by the word of their testimony; and they loved not their lives unto the death. 12Therefore rejoice, ye heavens, and ye that dwell in them. Woe to the inhabiters of the earth and of the sea! for the devil is come down unto you, having great wrath, because he knoweth that he hath but a short time.
We see two things here, a "REJOICE" and a "WOE." Rejoice to "ye that dwell in the heavens", but WOE to the inhabiters of the earth, because the devil is come upon down unto them. The manchild is not an inhabiter of the earth. This reminds me of what Paul said, "But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his." (Romans 8:9)
Also: "And hath raised us up together, and made us sit together in heavenly places in Christ Jesus" (Ephesians 2:3)
We see that when the Devil is cast to earth, he persecutes the woman. And we also saw that "the bretheren" with the testimony, "loved not their lives unto death." In other words, the bretheren are within the woman being persecuted in the earth, even though the seed of the woman is in heavenly places.
The seed of the woman are persecuted in the earth, but the whole time, they are raised unto God in heavenly places and so endure their persecution without revenge or malace and without falling away from the faith, because they are kept by God and the woman is fed while she is in the wilderness.
As part of the testing of the saints, WATER flows from the dragon's mouth as to carry the woman away. I believe when we see "mouth" in Revelation, it speaks of doctrines and teachings, and I believe in this case, it is false doctrine concerning "water" (Spirit of Christ) as Eve was taught false doctrine about the "tree of life" (Spirit of Christ). But the "very elect" cannot be deceived.
So here is who I see to be the manchild:
17And the dragon was wroth with the woman, and went to make war with the remnant of her seed, which keep the commandments of God, and have the testimony of Jesus Christ.