I believe as you that infants and children who have not reached the age of accountability at the time of the Rapture will be raptured. However, since all adults who have been raptured will serve during the Millennial Reign of Christ on earth in our new glorified bodies, then what will happen to the infants and children? I would imagine that glorified bodies will not grow, therefore how will these raptured babies and infants be able to serve during that time, or in what form will they exist?
I realize your answer will be speculation, as I don’t know of any scripture that would answer this question. It’s just one of those things that came across my mind, but obviously, isn’t deemed very important by God for us to know until the proper time.
The Bible doesn’t address these issues directly except to imply that the way things are here are not necessarily the way they’ll be there. All we know is that we’ll recognize each other and we’ll have eternal glorified bodies, and that everything required for our happiness will be available to us. To me that means that no one will enter eternity with a condition that would limit his or her eternal happiness, such as incomplete physical development might.
By the way, the Bible doesn’t say that we’ll serve the Lord on Earth during the Millennium, but that we’ll reign with Him, and our home is the New Jerusalem, which is located near Earth but not on it.