Justin and Hailey Bieber Add to the Family with Adorable Puppy Named Oscar

Justin and Hailey Bieber are now a family of three ... after the addition of an adorable little pooch just in time for the holidays.

Hailey shared the big news on Instagram Saturday, posting a pic of her "Christmas baby" on her story ... a puppy named Oscar Bieber. It's hard to say for certain, but it looks like he's a Maltese Yorkie.

Hailey also shared a vid of the lil pup on her bed playing around with Justin and a pic of Oscar sleeping ... yep, pretty frickin' cute.

The recently wed couple have really been enjoying the honeymoon phase lately -- kissing at hockey games, shirtless piggyback rides, etc. -- so it's only natural to take their marriage to the next level and get a dog.