"It just made sense for them," a source tells PEOPLE. "Eddie's lease was up and LeAnn's home was bigger and already familiar to Eddie's sons." (Cibrian shares custody of Mason, 7, and Jake, 3, with his ex, model Brandi Glanville.)
"It's somewhere the kids know and it allows Mason to stay in the same school district, which was important to them, that there's continuity for him," the source says. "They take [moving in with the kids] with a lot of responsibility. They want to make sure that it was done in the right way."
According to the source, the move to the gated community in L.A.'s San Fernando Valley won't "be an overnight thing," but will happen over the course of the next month.
Rimes's rep confirms the news, telling PEOPLE, "they're excited for this happy new journey."
The country singer, whose covers album Lady and Gentlemen is due Oct. 5, is excited to let Mason and Jake decorate two of her former guest bedrooms so they can feel at home, says the source, who adds that the boys "love LeAnn's dogs, and the swimming pool and the backyard."
With Rimes's divorce from chef Dean Sheremet finalized in June, and Cibrian's divorce pending, could an engagement be on the horizon?
Says the source: "They're just enjoying the moment and are hopeful about their future together."