What about having a child-like faith, you ask? Aren't children ignorant of many things and innocent of sophisticated ways of thinking and argumentation? Jesus just wants us to "have faith," doesn't he? If you read Matthew 18:1-3, you'll see that Jesus isn't telling us to become like children intellectually, but rather that if we want to be "great" in the kingdom of heaven (18:1), per the disciples' question, then we have to become like children in the sense that children are dependent on others for their sustenance. "They are dependent upon others and willingly accept from them what they cannot provide for themselves."  Jesus compares being like children to being like the kings of the earth (17:24-27), telling his disciples that greatness is not a social status or set of reigning powers bestowed by aristocratic means. Rather, it means being converted (turning to God in faith for life, forgiveness and entrance into his kingdom), as opposed to seeking the so-called glorious power of kings.
 New Geneva Study Bible, Nashville: Thomas Nelson, 1995, p.1535.