“How does he respond when you tell him ‘no’?”

Oliver’s physical therapist first posed this question a month or two ago — back when our son, perfectly content to sit and watch “The Muppets,” was still so easy to entertain. He was not crawling, was barely rolling. Ollie could sit independently, but was only just beginning to scoot to find interesting toys to grab.

My husband and I glanced at each other. “Well, we’re not sure yet. We never say it.”

My, how quickly things change.

Overnight, it seems, our 13-month-old is a man on the move. He can crawl at a surprising clip, pulling open cabinets before Spencer and I have had the chance to lure him back with a talking robot or favorite book. More worrisome is his new talent for pulling up and climbing onto anything and everything: any ledge his chubby hands can grab. The couch, coffee table, windowsill, a low rung of his high chair . . . and as he gets his sea legs, Ollie has started planting his hands against the wall and simply inching to stand. By himself.

Where are you going, Oliver?
Come back, Oliver!
Oliver. No stairs!
Mommy said no, Oliver.

And that’s in a five-minute span. Welcome to parenthood, right?

You’d think I would have been more prepared for this. Because Ollie was slower to develop than your “average” (whatever that means) child, I guess, our baby stayed a baby even longer. We had additional months to baby-proof and prep, but . . . yeah. No. As soon as Oliver took his first halting moves forward on his hands and knees, I knew we were in trouble.

Gates have been purchased. Locks have been installed. Outlets all covered.

And when I watch my cherubic child stumble, I have to tamp down every gut reaction to keep from holding him steady.

One of the hardest parts of parenting has been knowing — knowing — he can fall, he can hurt himself, and having to stay close but not too close to allow some of that to happen. I’m not talking obvious danger, of course — but when he’s scooting along the edge of the couch, I know there is a probability of him landing on the floor. He will cry, and I will comfort him. And he will, of course, stand up again.

Children are resilient. They let so little stop them. They are bold, unafraid — and I have to remind myself that Ollie isn’t inhibited by minor things like the laws of gravity.

He wants to try, to move. And we have to let him.

Before I stopped reading baby books (they made me too anxious), I read somewhere that our job as parents is to let them safely explore their world with minor interference. I don’t want to trail behind my son taking everything away, scolding and scoffing and guiding him back to a tiny “secure” plot of blanket in the living room. But I also worry, of course: worry about how to keep him safe. What parent doesn’t?

The babyproofing is an ongoing project. I’m fighting the urge to lay bubblewrap across the hardwood floors, relying on it to break the falls that I cannot.

Not practical, of course. But don’t they say necessity is the mother of invention?