Carrie Underwood's stories of her son Isaiah singing "Little Drummer Boy" with her for her My Gift album have brought a lot of smiles and joy to her fans' lives this holiday season, but an update brings some sadness.

The childlike way the now nearly 6-year-old Isaiah sings "pa-wum-pum-pum-pum" has vanished. "He now pronounces his “Rs,'" she tells Taste of Country and select media. "He says 'pa-rum-pum-pum-pum' when he sings it now, which is very sad to me ... It's like that moment is already gone."

They grow up so quickly, don't they?

The song has been a spotlight track on Underwood's new Christmas album and Isaiah's performance a highlight of her HBO Max Christmas special. To premiere the film, Mom says they rented a theater and watched together as a family, but one song after his performance, Isaiah was more or less bored with it all and wanted to go home.

“I think he was pretty happy with it," the singer says of this new version of "Little Drummer Boy." "He went to school and told all his friends about it and they listened to it in class. I think he's proud of it."

Previously Underwood gushed about how special that moment in studio was for her and how her boy even dressed up for the occasion, proudly stating that he was singing for Jesus. Isaiah's innocence — and an audio memory of his voice at age five to pull back up when he's a grown man — are what she'll take away from this year. Her oldest son knew nothing of the industry or No. 1 songs or expectations.

“He just knows that he's singing and being joyful and happy doing it, which was such a joy for me to watch," she shares.

Underwood has done numerous interviews in the last two months and has talked frequently about her holiday plans. It was husband Mike Fisher who shared what she was getting for Christmas. See for yourself at the video below. Fisher and Underwood also have a son named Jacob who turns two in January.

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