Jason Aldean's little ones, Memphis and Navy, are 'pretty much twins'

There's been a lot of celebrating at Jason Aldean's house lately.

His son Memphis just turned two on Sunday, and today, his daughter Navy is 10 months old.

"They're pretty much twins, just only born about 14 months apart," Aldean tells ABC News. "But they look really similar."

Aldean, 42, and his wife Brittany told People last year that they planned to have children close together. The couple, who underwent in vitro fertilization to conceive both of their children, wanted to "knock it out... while we're used to having one in diapers and formula."

“I think it’s tougher when you get out of that and wait a couple years and then have to go redo it all," Aldean, who has two daughters from a previous marriage, told People. "We just wanted them to be close in age, and we figured we’re already in that mindset now, so why not?”

Now, he tells ABC News, he knows that decision was the right one for his family.

"It's been a lot of fun having two little ones at the house," the ACM Entertainer of the Decade reflects. "And, you know, it's exhausting, but it's a lot of fun. And it's cool to have them there."

"This will this be her first Christmas with us, you know, so I'm looking forward to that as well," he adds.

There's plenty for Aldean to celebrate on the career front too. His new album, "9," debuts at the top of the country albums chart this week, as its debut single, "We Back," nears the top ten.

This weekend, Aldean will play a three-night stint at Park Theater at Park MGM in Las Vegas.