Kourtney Kardashian -- Solo Parenting for Penelope's Birthday (PHOTO)

New ground for Kourtney Kardashian -- for the first time she's officially a single parent for one of her children's birthdays -- but she didn't miss a beat at Disneyland.

Kourtney celebrated Penelope's 3rd birthday by wearing matching Tinkerbell outfits with her daughter. Even though dad Scott Disick is MIA ... Grandma Kris (with BF Corey Gamble) and Aunt Kim (with North) filled in for the day in the park.

Let's be honest ... Kourt's had plenty of practice parenting on her own.

4:22 PM PST -- After the photos surfaced of Kourtney, Penelope and the Kardashians at Disneyland ... Scott has now posted a birthday message.