Sarah Michelle Gellar Shares a Rare Photo of Her Son Rocky — See the Cute Pic!

Sarah Michelle Gellar and Freddie Prinze Jr.'s little boy is growing up so fast!

The 39-year-old actress took to Instagram on Tuesday, Sept. 20 to wish her rarely-seen son, Rocky, a wonderful fourth birthday — and the pic she posted of her youngest child is too cute for words!

"I'm knocked out that you are already four-years-old! #HappyBirthdayRocky," Sarah Michelle began her caption. "'Sometimes when you pick up your child you can feel the map of your own bones beneath your hands… This is the most extraordinary thing about motherhood — finding a piece of yourself separate and apart that all the same you could not live without.' This quote is from one of my favorite authors and completely sums up the love I feel for my children."

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Sarah Michelle and Freddie, 40, welcomed Rocky in September 2012. The couple — who married in 2002 — are also parents to a seven-year-old daughter, Charlotte.

Click through the gallery below to see more of the cutest kids in Hollywood!