A: Your question is a really good one.
I'm sure that there is more to it than this. But here's my best effort at the present time. I think asking a lot of questions and being curious is definitely something that is characteristic of children. I know other interpreters I've heard discuss this passage also make a big deal about the simple trust that children often express in their parents. They say that we (as Christians) are to likewise have simple faith and total trust in God.
These are certainly true statements. However, I don't think that this is the intent of this passage. By making a big deal about these characteristics of children we are separating the verse from its context. I think they end up making a point that the Holy Spirit, through Matthew, was not trying to make. In my opinion, anyway! That's not to say that children aren't like this, at least in general, or that these things aren't true. I'm not saying that we shouldn't ask questions, be curious, or simply trust what God says! Of course we should.
I am a firm believer that we are supposed to get our meaning "out of the text" (a process called exegesis). We are not to read our meaning "into the text" (a process called eisegesis). We can make the Bible say anything and everything with the second method. Very dangerous.
In Mark (10:13-16) and Luke's (18:15-17) telling of this same event, they add "receive the kingdom like a child." This may point to the faith aspect of "receiving" the kingdom.
I think part of the meaning of this being included is linked to the disciples. Jesus says it to them. It is in response to their conduct. They were rebuking people for bringing children because children were not valued in the culture. At least, not as children... they were valuable because they would grow up and become adults. The disciples would prefer to wait until they are older and more important before they come and bother Jesus. It would seem like a waste to them for a Rabbi to spend his time with some kids. But Jesus responds that the kingdom belongs to "such as these." That is, the kingdom belongs to those whom the world does not esteem. This same truth is taught elsewhere in Scripture which emphasizes God's heart in the gospel:
But God chose the foolish things of the world to shame the wise; God chose the weak things of the world to shame the strong. He chose the lowly things of this world and the despised things--and the things that are not--to nullify the things that are, so that no one may boast before him. It is because of him that you are in Christ Jesus, who has become for us wisdom from God--that is, our righteousness, holiness and redemption. Therefore, as it is written: "Let him who boasts boast in the Lord." (1 Corinthians 1:27-31, NIV)
If the character of children is in view (which I don't think, but it's possible), then there is another aspect of how kids behave that is important. I've seen it in my own children recently. They really have a heart to spend time with their "daddy!" My kids love to spend time with me. They want to be with me. I am often convicted when spending time with my children - I lament that I'm not always as excited to spend time with my heavenly Father as they are to spend time with me!
We are told to love God with an undivided ("all") heart and mind. Children are the closest thing I've ever seen to having a "single eye" and intention when wanting to spend time with their parents. It fades over time. Eventually kids (usually in the pre-teen stage and beyond) begin separating themselves from their parents. Before that, however, it really is amazing to see how loyal and dedicated children are to spending time with and having the attention of their parents.
Despite these interesting tid bits about the character of children and my own personal "object lesson" from God in the recent past through watching my own children, the intention of this particular teaching of Jesus seems to be focused less on the "children" and more on those who would try and keep the "less important" people from coming to Jesus. If we hope to receive the kingdom, we must confess our own unworthiness to earn it and receive it as a free gift of a gracious and loving God. We must also never try and restrict people from coming to Jesus based on our own judgments of who is worthy and who is not.
Remind the people to be subject to rulers and authorities, to be obedient, to be ready to do whatever is good, to slander no one, to be peaceable and considerate, and to show true humility toward all men. At one time we too were foolish, disobedient, deceived and enslaved by all kinds of passions and pleasures. We lived in malice and envy, being hated and hating one another. But when the kindness and love of God our Savior appeared, he saved us, not because of righteous things we had done, but because of his mercy. He saved us through the washing of rebirth and renewal by the Holy Spirit, whom he poured out on us generously through Jesus Christ our Savior, so that, having been justified by his grace, we might become heirs having the hope of eternal life. This is a trustworthy saying. And I want you to stress these things, so that those who have trusted in God may be careful to devote themselves to doing what is good. These things are excellent and profitable for everyone. (Titus 3:1-8, NIV)
Amen! Thank you, Lord!