By Meghan Leahy

Special to The Washington Post

Q: I have a very happy, optimistic 9-year-old who is also the youngest. The downside to all that happiness and optimism is that he seems to live in a bubble in which he thinks nothing bad will ever happen. Last night, I saw him cross the busiest street in our neighborhood, on his bike, without looking at all. It was a heart-stoppingly terrifying moment.When he got home, I sat him down and made him watch a few YouTube videos of kids getting hit by cars (dash cam and surveillance footage, so it was jarring and horrible but no blood or guts). I tried to communicate urgency and sadness, rather than anger. It upset him and he cried, but at least I know I left an impression. Still, is there a better way to instill in him a sense of vigilance?

A: So what are we going to do about this little daredevil of yours? He has demonstrated to you, without a doubt, that he is not mature enough to ride his bike near major intersections. You saw it with your own eyes. And while it seems all of America is abuzz about allowing failure in childhood, we all know better than to allow failure when safety is at issue.

Failure, in this instance, equals severe injury at best, death at worst.

And as maddening as what I am about to tell you is, it is the truth. You cannot “teach” vigilance to a child.

I would love to assure you that he watched those crash videos and took in your advice. That he gained some kind of experiential wisdom and will now slow down and look both ways.

Sorry. Nope.

The brain doesn’t really work that way. Did you scare him? Sure. Did he take in how upset you truly were? Maybe. It still doesn’t mean his brain is any more mature or vigilant.

For very sensitive children, these videos and lectures can have some effect (in terms of a behavioral outcome), but for most children the message of safety doesn’t sink in.

Why? The growing brain of a child works with both repetition of experience as well as traumatic experiences. Meaning, when you say “no” to the cookie over and over and over, the brain will register to the child, “Hey, Mom ain’t giving you a cookie at 5 p.m.! Stop asking!” That’s repetition.

In a traumatic event, the experience is so jarring and so upsetting that it can change the brain. Literally. The brain holds on to the trauma, but often not the memory of trauma. There are children who witness horrible accidents, for example, and it changes how they react to a number of stimuli in a way that could appear irrational to the average person.

For your son, we cannot allow a traumatic incident to occur. It is our parental duty to not allow him to be hit by a car.

Thus, he is not allowed on a bike anywhere near an intersection.

This will upset him greatly. He will feel like he is being treated like a “baby.” He might negotiate, yell, try to break the rules, beg and become insolent. So be it. The alternative is not acceptable.

While you are busy holding this boundary, you will also help him become more vigilant.

When he wants to ride a bike near an intersection, you have to be with him. That’s the rule. That will horrify him — but maybe that will help him remember more.