As he watches his three daughters grow up, the singer tells how he's learning from them — and the most important lesson that he and wife Lauren are teaching

In his year off the road, Thomas Rhett says, he's learned lots of life lessons, and his best teachers have been the three little girls who call him Daddy.

"I'm not a very organized person, but when I make a plan, I need to see the plan come out exactly how I planned it — and when you have three kids, that's just impossible," he tells PEOPLE for a story in this week's magazine.

"I could plan to go to the beach tomorrow and then someone will wake up with a stomach virus, and I have to be okay with that. The biggest way that I have grown is learning how to laugh through that stuff rather than get frustrated with it. That's been a huge change that took quite a bit of work, but man, things just don't frazzle me as much as they used to, and it's just such an easier way to live when you're not so concerned with the little stuff."

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Thomas Rhett with his family
The Akins Family
| Credit: Grayson Gregory

Instead, the 31-year-old artist says, he's finding what's most important as a parent is simply staying in the present — and that means seeking out special moments with each of the daughters he shares with wife Lauren Akins: Willa Gray, 5, Ada James, 3½, and Lennon Love, 14 months.

"I just love getting to spend one-on-one time with each of them, which is something that I didn't think was really important before," he says. "I just thought as long as the five of us were together, we were good. But I think the longer I've gone as a dad, it's like each child really does need that one-on-one time — in the same way that Lauren and I just need time with each other."

Now, he says, taking Willa Gray for an ice cream cone is "the best thing ever," and he loves to turn his home studio into a playground for the girls. "They all love music, and they all love to go there separately," he says, "and I'll just get a guitar and they'll bang on the piano, or I'll pull up my Pro Tools rig and put some drumbeats on there. And they'll just sit up here and play."

thomas rhett and lauren akins with their family
Willa Gray, Thomas Rhett, Ada James, Lauren Akins and Lennon Love
| Credit: Thomas Rhett Akins/Instagram

Among his joys is watching each girl's personality develop. "Willa Gray is a mother spirit, a nurturer spirit," he says. "If Ada James or Lennon is crying, she's the first one over there to be like, 'Are you okay? Do you need your blanket? You want me to get you a bottle of milk?' Then you've got Ada James, who is extremely sassy. The first person to say, 'Hey, baby, let's go get on our pajamas,' gets 'Well, I don't really want to right now.' And then you've got Lennon, who's just starting to talk, and she's just as much of a firecracker as Ada James. They're all so different, yet they're all so loving, and they all have their own unique personalities."

But all, he says, are getting the same message from their parents. "We preach kindness like it is our job," says Thomas Rhett. "That's our standard. 'We treat people with kindness, and we treat people with love' — and that's what we say in their prayers at night."

At the moment, he notes with a chuckle, the words aren't quite soaking in to his "sassy" girl: "I can't tell you how many times a day I look at Ada James, and I'm like, 'Let's be kind!' And she's just like ..." His hand flies over his head. "But she is 3," he adds with a knowing smile.

RELATED VIDEO: Thomas Rhett Hopes His Daughters 'Will Take the Lesson of Kindness' Into the World

Even at their young ages, Thomas Rhett says, he feels time with his daughters is flying by. "There's that saying of 'the days are long and the years are short,' and I've never heard a truer statement as a dad," he says, "because you get into these days, and they feel like they last a year, and then the year's over and your child is already a year older."

No doubt he senses the teen years aren't that far away, a fact underscored by a song on his new double album, Country Again, "To the Guys That Date My Girls." (Side A debuts this Friday, and Side B will be released later this year.)

Thomas Rhett Country Again - Side A
Thomas Rhett
| Credit: The Valory Music Co.

Thomas Rhett co-wrote the poignant ballad with the girls' grandfather, dad Rhett Akins (along with Will Bundy and Josh Thompson), and its chorus summarizes the preciousness of a dad's love: "I know that they won't be young forever / but I'm gonna hold on as long as I can / So when you take their hand, remember you're holding my whole world / just a friendly reminder to the guys that date my girls."

Thomas Rhett confesses he's already dreading the day each of his children grows up and leaves home. "Man, I have a hard time thinking about their futures because I don't want them to go anywhere, to be honest with you," he says. "I just want my kids to get out and make a way for themselves knowing that they can come home anytime they want to."

Thomas Rhett with his family
Lennon Love, Lauren Akins and Thomas Rhett
| Credit: Grayson Gregory

And, he says, exactly how many children that will be has yet to be determined. "My wife has wanted five kids for forever," he says, "so I'm sure we're gonna have at least that many."

Willa Gray, for one, has already been asking for another sister, he reveals. 

Not a brother?

"Yeah, well, you know, I would love a son," Thomas Rhett allows. "But at the same time, I'm so used to embracing this 'girl dad' life that I don't really know what I would do with a boy, to be honest with you!"

For more on Thomas Rhett and Country Again: Side A, pick up the latest issue of PEOPLE, on newsstands everywhere now.