Christina Aguilera says her baby daughter Summer Rain and son Max are getting along so well that they're already BFFs! Credit: Trae Patton/NBC/NBCU Photo Bank

If this keeps up, Christina Aguilera might just have a built-in babysitter in eight or nine years! The "Stronger" singer, who welcomed daughter Summer Rain with fiance Matt Rutler in August 2014, says the infant is already getting along famously with her big brother, Max.

"He's so endearing and sweet to her," Aguilera, 34, told Extra of her son with ex Jordan Bratman. "He's in school, he's 7, there's a little age gap, but it's perfect though, because then they don't fight over toys, but he's the big helper and the big teacher," the kids' doting mom said. "I'm like, 'How old are you?' He's like a grandma to her, he's just like, 'I'll teach you everything.'"

Aguilera's only request during Max's hang time with his sis? He's got to hit the sink first! "The only thing [is that] I'm like, 'Wash your hands before you touch the baby' — you don't want the germs," mom explained.

For her part, 5-month-old Summer Rain is fitting in just fine at the Aguilera-Rutler household. "I have a chill baby — she's just so calm and so easy to make laugh and smile," Aguilera — who posted an adorable photo of her little girl with a "diva" diaper on Instagram to debut the tot to the world in January — said. "She's just a breeze, thank God!"

 

 

With her son already in second grade, Aguilera clearly loves having a newborn at home. "Her little tushy! Those chunky legs. I love it, I love to nibble on them!" she enthused to Extra.

Set to return to The Voice for its next and eighth season, Aguilera has been juggling parenting a newborn with recording her new album. "I'm very excited to pour my heart out into this record fully. I've been gathering and writing and coming up with these amazing ideas for different parts of how I was feeling the past year, so I'm really excited to vocalize all of it and make it all come together," Aguilera — who is currently working with Pharrell Williams on the new disc — said. "[My new music] is genuine and heartfelt."