Couple Brad Pitt and Angelina Jolie spend their Valentine's Day visiting the Natural History Museum in Los Angeles, California with their twins Knox and Vivienne on February 14, 2013. Credit: Dmac/Premiere/Rocstar/FAMEFLYNET

Benjamin Button effect! Brad Pitt's youngest son Knox is looking more like him every day. The 4-year-old tot dressed up just like his dad, 49, while visiting the Natural History Museum in downtown Los Angeles on Valentine's Day. The two were joined by Knox's twin sister, Vivienne, and Angelina Jolie, 37.

The father and son both styled all black ensembles consisting of a coat, T-shirt, pants and sunglasses. Knox even has his blonde hair grown out to the same length as Pitt's famous 'do.

The stylish family -- minus Maddox, 12, Pax, 8, Zahara, 7, and Shiloh, 6 -- had a bodyguard in tow, but received no special VIP treatment as they arrived at the museum, a witness told Us Weekly. Heading straight to the dinosaur hall, Pitt, 49, and his mini-me held hands while touring the discovery center. (See more photos of Brad, Angelina and Knox from Valentine's Day!)

"Brad was walking around reading to Knox and explaining things to him," the observer told Us.

And the adults had just as much fun as the kids. "Brad and Angelina stood back at one point and let the kids play," the witness told Us of the parents of six, who have been engaged since early 2012. "They were smiling and really enjoying the day -- you can tell they love watching their kids learn."