Here, the play on words here is lost almost entirely in translation. First, notice the tenses. The "will lower himself" is the future tense but the "is the greatest" is the present tense. Does this mean that Jesus sees the realm as coexisting with earth or that everything in the realm of the skies is in the present tense?

The verb translated as "humble/takes a lowly position" means "lower." Jesus only uses it three times. The realm of the skies is obviously higher than earth so we would assume that the greatest is also the highest, but Jesus says that the greatest there is the lowest. The word "little child" is more emphasized in Greek. the play on words here is that "greatest" also means "full grown."   In this case, when you lessen yourself on earth, you don't become great but are great in the higher realms. If you can grow into a child on earth, then you are an adult in the higher realms. .