Stepmom-in-training!

As Kelly Clarkson goes into 2013 planning her wedding to boyfriend of nine months Brandon Blackstock, the singer is also preparing for another life-changing milestone: she'll officially become the stepmother of her talent manager fiance's two children -- Savannah, 11, and Seth, 7 -- from a previous marriage.

"Kelly pays special attention to them," an insider tells Us Weekly of Blackstock's kids with ex-wife Melissa. One way the "Stronger" songbird spoiled them? The trio went on a VIP tour of Disneyland last summer when Clarkson was on a break from filming ABC's Duets.

Though she is intent on making a good impression on Savannah and Seth, Clarkson, 30, is "careful not to step on their mother's toes," says another insider, adding that American Idol's inaugural champ "definitely wants to have some of her own kids with Brandon."

Accepting Blackstock's proposal -- and a 6-carat canary diamond! -- on Dec. 14, the Burleson, Texas native once talked about eloping with her man, but pals say she's now focused on a much more public bash.

Inspired by Blake Shelton** and Miranda Lambert**'s 550-guest Texas bash in 2011, the engaged Southerner "wants to go all-out," says a friend. "She'll keep it country, though."

Regardless of the scale of their bash, Shelton expects an invite. "I told Brandon, man, you need to grow up and figure out that you need to marry this girl," Shelton, speaking to Hollyscoop, recalled telling his manager Blackstock. Now that the couple is engaged, Shelton is offering up his services as a wedding singer. "I am going on the record saying, I will do the music at the wedding or whatever you want to do, I'll be that guy."

This article originally appeared on Usmagazine.com: Kelly Clarkson: Inside Her Special Bond With Fiance Brandon Blackstock's Kids