[UntoHim]

First of all the Lord Jesus was talking about being as a child is relation to being humble and simple in our faith, and not how we would do theology.

the last Adam became a life-giving "x"
The trinity = "x:
(x = unknown)

Actually neither "x" is unknown...well, it's not if you really want to take the Word of God seriously, and let the Bible interpret the Bible. Of course, if you think the Bible is nothing but a bunch of fairy tales and religious gibberish, then everything is "x" to you anyhow, and searching for the mysterious "x" is a gigantic exercise in futility.

But for anybody who is serious, the apostle Paul gave us the most clear explanation of our future eternal existence as there is before us in black and white. He plainly laid out the beginning - "the first man Adam became a living soul". The account in Genesis is simple and clear: The Lord God...breathed into his nostrils the breath of life, and the man became a living creature. Then the apostle Paul lets us know that this was not the end, but rather only the beginning. The life that was imparted was only the seed. "It is sown a natural body; it is raised a spiritual body. There is a natural body, and there is a spiritual body." Very simply, "THERE IS A SPIRITUAL BODY" - Amen. There is a spiritual body. The first Adam received a "natural body", and the Lord Jesus, as the second Adam, became the forerunner of all who will receive a "spiritual body".

There is LOTS more to delve into here, but I think I have somewhat accurately, albeit incompletely, given us an initial outline with which to start with. Again, I must emphasis that everything we need to work with is found in the actual biblical text itself. We can use some external material, but only if that material does not lead us astray from, much less contradict, what is plainly and clearly presented to us in the actual text.