How can Riley Mesnick be 1 year old already?!

Presumably Jason and Molly Mesnick are asking themselves the same thing, but the onetime Bachelor couple aren't sweatin' it. They made the most of their little girl's milestone last weekend with a big birthday party at their house attended by about 100 family members and friends, including former Bachelorette Desiree Hartsock and fiancé Chris Siegfried.

"I loved seeing Riley interact with all of our friends and family during the party," Molly exclusively tells E! News. That many guests "can be quite overwhelming for a kiddo, but she handled it like a pro! She was eating up all of the attention that she was getting!"