One claim that I have heard advanced is that children, while being capable of sin, are more often guilty of childishness than disobedience and rebellion.
While it is probably often the case that children are frequently childish, and less frequently sinful, the ability to discern the difference is important. Perhaps more important is the responsibility of parents to address childishness rather than use it as an excuse.
Let us take an example of a situation that doesn't involve sin, per se, but simply childishness that a parent ought to be working toward removing in an effort toward maturing the child. Children are perpetually running, laughing, being loud, and being relatively unobservant of whatever else is going on unrelated to their immediate desire. All of these things are obviously childish, and often in a way that is healthy and worth encouraging, as opposed to unwise or unbecoming. However, there are many situations where children ought not to be running, laughing, being loud, or being unobservant of their surroundings. Some of those situations involve the safety of the child (let us say, playing near a busy street) while others involve showing courtesy and loving consideration of others (let us say, prior to church when people are entering and greeting one another).
Suppose little Johnny comes into church with Mom and Dad and begins to tear away from them in order to go run around with Billy whom he sees across the foyer full of people in the midst of conversations. Johnny doesn't ask permission to leave, but runs across the room, brushing past some and bumping into others until he reaches his destination. Along the way he begins yelling at Billy at the top of his lungs in order to get Billy's attention. Everyone hears Johnny, most see him, and several are physically bombarded by his presence. Is Johnny being disobedient or rebellious, or is he just being childish?
The answer is, it depends. It depends upon what the parents have done to prepare Johnny for the situation in which he finds himself. Have Johnny's parents taken thought of what they want Johnny to look like when they enter the building where the church meets? Have they communicated that picture to Johnny and practiced it with him in order to train him for success when he enters into that situation? Have they reminded him prior to entering the building of what they expect from him? If the answer to any of these questions is, "no," then Johnny's actions bear more upon his parents' wisdom than upon his own. However, if Johnny's parents have diligently trained him and given him what he needs to succeed in the situation, and Johnny allows his passions to rule over his parents' training, it is more likely that Johnny is disobedient rather than simply childish.
And it is here where the explanation of childishness tends to be used as an excuse for parental foolishness, or even outright parental abdication and sin. God has placed Johnny in his parents' home in order for those parents to prepare Johnny to think and act wisely in the world. Not only wisely, but in a manner that pleases God, which, at its core, involves putting the needs and goods of others before the needs and goods of oneself. By allowing Johnny to run roughshod through the church, interrupting numerous conversations, and putting himself and others at mild risk of injury demonstrates a lack of foresight at best, and willful negligence at worst. In other words, the parents who witness such behavior and take no steps towards growing Johnny into the maturity to handle the situation wisely are parents who are hating Johnny rather than loving him. Moreover, they are parents who are despising the gift that God has given to them to invest well, as a talent, we might say.
Parenting for those who have little experience, poor teaching, no real training, and a host of other likelihoods in our present day and age is an embarrassing endeavor. All the better for those who are willing to be humbled by embarrassment rather than pridefully excuse it with recourse to their children's natural immaturity. My wife and I have witnessed far more situations where we have failed to think ahead and prepare our children well than we have situations where we've succeeded with flying colors. More to our shame is the fact that we've grown angry and blamed our children for what is really our own foolishness, and at times, sinful omission. Failures have become opportunities in themselves to model repentance, pleas for God's pardon, and receiving forgiveness and restoration. They've also been instructive on where our own thinking, training, and doing require sanctification.
It should be stated that the process of training a child for any situation is just that, a process. And because it is a process that involves the messiness of sinners on both the side of the trainers and the trainees, there are lots of opportunities for grace and forgiveness to be shown, as well as discipline and confession of sin. If a married man and woman will often have moments where communication is difficult, or understanding is lost, how much more so parents with little developing minds of children. Nevertheless it is incumbent upon parents to be always thinking of ways in which to prepare their children for full maturity. Our own propensity toward inertia almost insures that they'll spend far more time being childish (in the good way) than they will be getting trained for maturity. Those parents who have a great measure of faith will find ways to make the training so much fun that the children don't even notice that they're being prepared for life as a responsible and capable human being.
Behind the preparation of children lies the principle that hard work in the right ways brings dividends of great and long-lasting proportions. Training a child how to see basic needs around the house and take care of them without being asked doesn't just make a child a good child. It will make him a great husband, or her a great wife. It will make him a great boss, or her a great coworker. Teaching a child how to listen well the first time doesn't just make parenting easier, but it makes for an adult who is less likely to make mistakes and more likely to lead others well.
It will be a culture on the path to great harmony and prosperity that recognizes childishness as something to be fashioned and directed, rather than something to be excused and smiled at as an inconvenient, but naturally outgrown set of attitudes and behaviors.