Wow, after just 24 hours together they’re already besties! Carrie Underwood, 35, and Mike Fisher, 38, welcomed their second child into the world on January 23, and their 3-year-old son Isaiah is already loving being a big brother to the baby boy. A source told Life & Style exclusively how the pair is already bonding.

“Carrie and Mike couldn’t have been more excited about introducing their son Jacob Bryan to the world,” said the source, and the same goes for little Isaiah! He’s “already itching to play with Jacob.”

Isaiah and Mike Fisher with Baby Jacob

Isaiah and Mike Fisher with Baby Jacob

“Mike’s been explaining to Isaiah that he needs to wait a few months before they can roughhouse,” the insider explained. “It’s no secret that Carrie wanted a girl, but two boys is also a dream come true. Isaiah calls Jacob his little partner in crime, it’s super adorable.”

We’re sure they’ll be getting into shenanigans together in no time, and it sounds like they’ll have plenty of opportunities to spend time together when they’re on the road with mama. “Carrie’s Cry Pretty 360 Tour starts in May and she’s already planning on her boys traveling with her,” the pal confessed.

But right now, it’s all about taking care of baby Jacob, and getting him adjusted to his new life. Luckily, it sounds like he’s already doing great! “He’s the cutest thing ever and the family couldn’t be happier,” said the source. “He’s happy, healthy and already smiling.” What more could new parents ask for?

Of course, we would be remiss not to mention the third musketeer in this new sibling duo: Zero! Just days before welcoming their baby boy, Carrie and Mike adopted a German Shepherd puppy who will play two important roles in the household — Jacob and Isaiah’s pal, and security guard! “Isaiah affectionately named him Zero. I guess it fits because it’s the chance of surviving if you try to break into our home,” joked Mike. We can’t wait to watch all three of these cuties grow up together!