Sarah Michelle Gellar celebrates her kids' back-to-back birthdays

Sarah Michelle Gellar and Freddie Prinze Jr’s kids are growing up too fast.

Over the weekend, the Scooby-Doo costars — who tied the knot in 2002 — celebrated the back-to-back birthdays of their daughter Charlotte and son Rocky, who turned 17 and 14, respectively.

Charlotte’s birthday came first on Saturday, September 19, and Gellar took to Instagram with a sweet tribute. “Yesterday was my best friend’s birthday,” she wrote in the caption accompanied by a sweet picture of the mother-daughter duo.

The proud mom continued, “I’m not sure how you are 17 already. You may have been the child that made me a mom, but now you are the person that brings out the best in me. (Not to mention my biggest champion) Thank you… for being you.”

A day later came Rocky’s birthday, who was born three years after his elder sister.

“And then, there were two,” Gellar wrote in Rocky’s birthday tribute. “Three years and one day later @rockyprinze came racing into our lives. I should have known from your speedy delivery, the excitement you would bring. You have no idea how lucky I feel to watch you chase your dream. You inspire not just me, but everyone around you. Happy Birthday Rocky.”