My wife and I got married in 2004. When we said “I do,” her daughters were ages 19, 13, and 10. I went from bachelorhood to instant family.

It wasn’t so hard. There were no diapers to change, no spit ups to clean, no strollers to push, no baby clothes, gadgets or toys laying around the house. Instead, I just had to deal with the growing pains of girls who were teens and pre-teens going on 30.

Tara, the oldest one, didn’t live with us much, spending most of her time on her own. But when she needed us, my wife Sharon and I were there for her.

And so it was last Easter when Tara needed to move back home with her baby daughter, Arianna. She was just 6 weeks old; a tiny bundle, yet kind of big for her age. It was a huge adjustment for all of us. It took a few weeks, but we had a room built in our basement for Tara and the baby.

Kristen, my youngest stepdaughter, was excited to have an infant in the house, since she had always pleaded for a younger sibling — a plea that emphatically fell on deaf ears. Kelly, the middle one, started grooming Arianna to be a cheerleader and engraining in her Kelly’s love for Belle from “Beauty and the Beast.”

Having a baby around day after day has been a different experience for me — and a rewarding one: perhaps because I have yet to change a diaper.

In the summer and fall, Sharon and I watched Arianna at night while Tara worked and went to college. On nice nights, we took her — and our dogs — for a walk. Sharon had a much easier task of pushing the stroller than I had walking two excitable labradors.

We spent much of the walks just watching Arianna. She loved looking up at the sky and at the trees. And she was fascinated by street signs. She’d stare at a sign as we approached it, and turned her head to keep looking at it as we walked past. I suppose it was her first introduction to shapes.

One of the favorite things I do with Arianna that always gets a big smile is when I hold her on top of our refrigerator. She looks at everyone for a reaction, and starts laughing when my wife asks, “What are you doing up there?”

In November, Arianna began crawling — and she scoots. She likes when someone gets down on the floor to crawl around with her — especially when it’s her Pop-Pop.

But crawling was so yesterday. Now she wants to walk. And walk. And walk. At first, she looked like a drunk stumbling down the street. Now she could win the gold medal in the baby 100-meter dash.

Of course, that also means she’s getting into things she’s not supposed to.

The dogs have also benefited from Arianna’s presence as they perch themselves on either side of her high chair waiting for food to fall.

It’s hard for us to believe, but Arianna turned 1 on Saturday. It’s amazing how time flies when you see someone grow hour after hour, day after day.

Sharon and Tara both say I’m Arianna’s favorite and that she is a Pop-Pop’s girl. I don’t know why.

So her eyes get big and she giggles when she sees me walk into a room. Or that when I peek on her while she’s getting a bath, she starts laughing and splashing water. Or that whenever I come home, she reaches out for me to hold her.

Well, maybe Arianna is Pop-Pop’s girl.