Carrie Underwood Says She’s 'Very Proud' of 5-Year-Old Son’s Feature on Her Christmas Album (Exclusive)

Little Isaiah is featured in 'Little Drummer Boy' on Underwood's new holiday album, 'My Gift.'

Carrie Underwood is one proud mama! The country superstar released her Christmas album, My Gift, last month and it features one very special guest: her 5-year-old song, Isaiah.

ET's Rachel Smith spoke with Underwood ahead of the launch of her Calia by Carrie Underwood pop-up shops, where she expressed how proud she is of her and husband Mike Fisher's son. The American Idol alum explained that as she was working on the song she "could just hear his voice on it."

"He loves to sing…and he has such a giving, loving heart about him and I could just hear his voice on it," she told ET, explaining how at first she didn't know if he would want to do it. "So he goes in there and he just gave it his all and it's so pure and it's so special and he's throwing his hands in the air and just so expressive when he was singing it."

"I was so proud of him, just for giving it his all and the love in his heart because he does love Jesus," she continued. "At 5 years old he knows, and he was giving all the love. I'm very proud of him."

Underwood also shared that when Isaiah was listening back to his recording "he was so happy," but was also critiquing his work.

"I felt like in his little head...I was trying to read his face. I felt like he was like, 'Oh, I don't know.' Not like, 'I could've done better,' but there was something and I'm like, that is me in you for sure,'" the mother of two said, adding that both she and her son are perfectionists.

As for her Isaiah following in her musical footsteps, she said she would "definitely be supportive."

"For whatever it is that he's feeling like he's being led to do in life," Underwood related. "I think he's gonna be a person of many gifts and we're gonna see what he wants to do with them. If you ask him right now, it was something like an astronaut, a fireman, then it was like something ridiculous, like Spiderman."

Meanwhile, her time at home with her boys, which also includes 1-year-old son Jacob, has been filled with extracurricular activities. Underwood loves fitness and working out, and makes sure that her whole family also gets their bodies moving.  

"It's so important for them to get that physical time for themselves," she explained. "Hopefully as they get older, they will concentrate more on that and then we will be working out together."

As for her motivation for working out? It's "how I feel after I've worked out," she said of the fulfilled feeling afterwards. "It's probably more of a mental health thing than it is a physical health thing. I want to feel strong...I get to blow off some steam and this is my version of something self-care that I do for me."

Fans will get to workout just like Underwood with her latest Calia collection. Calia's fun pop up shops launched in Austin, Texas, Nashville, Tennessee, and Santa Monica, California, on Wednesday, Oct. 28. The shops, which will run through Dec. 31, will also feature the singer's music and Find Your Path book.

"I'm super excited. We've always had a large, beautiful display in Dick's Sporting Goods stores but this is just offering people a different way to experience Calia," Underwood shared. "And we're five years in. We're so proud of this collection. I feel like every time we roll out a new season, a new collection, it just gets better and better."

"I feel like a lot of people have found Calia helpful in their lives and the pop up shops are just super fun," she added.

For more on Underwood, see below.