And then, it was found. It was found in my lectionary group yesterday, and I am thankful to Jay, JodyBeth, and Keith for helping me find it. The link is submission to authority and discipline. Moses made soft the rule on divorce because the people were insistent on doing it their way. Their way led to marriages that were not mutually beneficial, which led to divorce (love wasn't really part of the equation yet).
Enter the kingdom of God like a child means realizing that God's way, the way of discipline and discipleship is better than our way. It means letting go of all the we've "learned" and getting back to the basics. Trusting that another has our best interests in mind, and doing what they command knowing that it will lead to the best possible outcome (today, tomorrow, and beyond).
The journey of discipleship is one of letting go our own ways and following The Way, it is the path of children.