Kelly's not only going to be a wife- she'll be a Step-Mom to Bandon's 2 kids too.

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.  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.

Kudos to the couple for keeping the kids out of the spotlight.  I tried to find a picture of the kids with the newly engaged couple to post with this story- there are none!

Click here for US Weekly's full story.