Jesus invited his disciples to be "as little children," innocent and pure and trusting. Paul, in his first epistle to the Corinthians, clarifies this doctrine: "in malice be ye children, but in understanding, be men" (chapter 14, verse 20). The idea that we ought to be adults is reinforced by other scriptures about growing up, rising up, becoming men, et cetera. But still, there's a sense of childhood that we need to remember and retain: that's what Jesus was talking about when he said things like "become as little children" (Matthew 18:3). So now we're left with a question. In what ways should we be like children, and in what ways should we not? In other words, what makes a child childlike versus childish?
The CHILDLIKE virtue of trust: children believe what their parents teach them. Eventually they start to question, and they kind of get addicted to it and question everything, but for the most part, children are a trusting breed. This is why parenting is such a big responsibility: kids' minds are malleable. What we can learn from this is that sometimes we don't have all the answers, but someone else might. Adults who forsake this ability to trust are bound to have relationship problems.
The CHILDISH vice of trust: "gullible" isn't written on the ceiling, your shoe isn't untied, and your fly's not open. When we learn to grow up and think for ourselves we will have to realize that we can't believe everything everyone else says. For example, when we build political opinions based on what our friends think, and not our own examinations of the issues, then we're acting as children, and not in a good way.
The CHILDLIKE virtue of imagination: children are extraordinarily imaginative. Their experience of "the real world" is limited, so they don't make the mistake of confining their imagination within real-world limitations. Children are like ancient Greeks; they explain phenomena through myth and stories. They don't rely exclusively on rationalism or empiricism to be satisfied. Their imagination's limitless nature, while often unrealistic, can lead to brilliant out-of-the-box ideas. And when nothing is impossible, they can say with Captain Kirk that they "don't believe in no-win scenarios."
The CHILDISH vice of imagination: it is common for a child to lack a sense of identity. Instead, they create fantastical and hypothetical identities for themselves (like in the film "Where the Wild Things Are," when Max convinces the wild things that he ought to be king - citing impressive yet imaginary credentials). This is what adults call "escapism," and while it might have its merits from time to time, it's a dangerous practice when overused. If our escapism replaces reality, we are childishly ignoring the real world and may neglect responsibilities, learning experiences, relationships, and more. Perhaps imagination should be like riding an airplane: sure, it's a wonderful journey through the skies, but you never get in a plane intending to stay among the clouds - coming down to earth again provides the journey with a useful and meaningful conclusion. For lack of a more sympathetic word, it's... functional.
The CHILDLIKE virtuous lack of malice: children are loving and forgiving. Children aren't racist until they're taught to be, and they don't hold grudges for long (probably thanks to a short attention span, but that's beside the point). Very rarely will a child hate or alienate another out of malice.
The CHILDISH vice of malice: when a child DOES feel malice, his anger is irrational and difficult to reason away. Plato said there were three parts of the soul: the reason, the emotion, and the appetite. The problem with children is the "reason" part of their soul (the part that really should govern us) hasn't fully developed yet, and their emotions are often left in charge. As adults, emotions are certainly important, but when we let them override reason, we are in a world of trouble.
In conclusion, we can learn a lot from children. The next time you're spending time with kids, try to take note of some things you should have outgrown (but haven't), and perhaps some things you should have never forgotten (but had). Hopefully we can all heed the counsel to "become as little children" while still trying to, "in understanding, be men."