Pakistan, Sept. 22 -- 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 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. Thank you for being you."

A day later came Rocky's birthday, who wa...