My daughter is about to turn 16. How is that possible? Soon, my baby will be eligible to drive. Who thought giving babies driver’s licenses was a good idea?

When Olivia was a newborn, I spent hours gazing into her tiny eyes, making silly noises and faces to coax out a smile. As my first child, those moments with her were unforgettable. Now, even as she performs on stage or navigates teenage challenges, I sometimes see the infant features in her expressions. It feels like just yesterday.

As an obligatory annoying father to a teenager, I often remind her, “You are my baby. You hear me? One day, you’ll be 50, and I’ll still say…”

Here, I switch to my old man impression, “Awww, look at you. My little baby.”

And in my best imitation of an older woman who chain-smokes, I’d have her retort, “Shut up, Pop! I’m not a baby.”

Her inevitable question…

Why do I sound like that?

Guess you’ll find out in 30 years.

Cue the eye roll.

Truth be told, those flashback moments are real when it comes to my little girl. She grew up before my eyes. I can’t believe it.

But…I kind of do believe it. After all, the universe has given me enough signs to know she’s older. The shows we watch, the jokes I tell her, and the conversations we have are all things that scream her age at me on a daily basis. I know she’s not a baby, despite the occasional time-traveling in my mind.

Her brother, though. Well, he’s an entirely different story.

Lucas, 13 and towering, might stand next to a genuine baby and look like Santa beside an elf. Despite his size and the static nature of our activities—Raffi, The Wiggles, and endless replays of Sesame Street—his world is wonderfully unchanging. He laughs at the same humor and enjoys the same routines, a comforting predictability that contrasts with his sister’s rapidly changing world.

It’s challenging to see him as the young man he is becoming when our days are filled with the familiar. In our home, he remains my baby, immune to the telltale signs of growing up that his sister exhibits. And I cherish that. He may always be my baby, regardless of age or size, and if we’re still watching Sesame Street when he’s 50, that will be just fine by me. It’s been that way for years. He likes what he likes. He always has.

While we don’t have conversations in the traditional sense, we interact verbally. I talk to my boy all day and every day. He comes to me with his device to ask for things or get me to come and watch TV with him. Again, these interactions have been the same for as long as we can remember.

That’s why it’s so hard to remember that this massive young man is a massive young man and not my baby. Sure, he visually looks 13, but that means nothing around here.

After all, he’s the only 13-year-old in our home. There’s no one to compare him to. In my mind, this round little dude, mere inches shorter than me, is what a baby looks like. It’s not until someone else brings a baby over that we get our glimpse into Santa’s Village. It usually takes a minute for my brain to adjust. I say the same thing every time.

Wow, Lucas is huge. I didn’t realize how big Lucas is.

The fact that our relationship has remained so similar as he’s grown also plays a role in all this. With shows, songs, books, and activities holding firm through the years, he is, in many ways, still my baby. He will also, in many ways, remain that way for the rest of his life.

And I love that about him.

Call it innocence or purity or whatever. He’s my little guy today and, barring any major milestone-smashing moments, he will be that way throughout our lives.

Still, it’s important to remember that he is 13 and I try to do that. His privacy is important and learning to trust him to make the right choices is just as important as it is for his neurotypical sister. He might not have the same responsibilities or expectations, but he’s still a teenager. He’s still growing.

Sure, he’ll always be my baby. Both my kids will be. The only difference is that he probably won’t protest in the imagined gravel voice I assign to his sister. Other than that, he’ll still be adorable at 50 and even if his tastes stay the same, it won’t change a thing. I’ll be there for him. I’ll be there for both of them.

They’re my babies. Whatever my babies want, I’ll help them get it, even if it’s an AARP membership card.