Brad Pitt and Angelina Jolie spent Valentine's Day (14.02.13) at the National History Museum with their children.

The couple took their four-year-old twins Knox and Vivienne to the dinosaur exhibit at the museum in downtown Los Angeles, where they enjoyed a fun family day out.

A source told Us Weekly: ''Vivienne loved the butterflies and Knox was interested in the dinosaurs and giant spiders. Brad and Angelina stood back at one point and let the kids play. They were smiling and really enjoying the day -- you can tell they love watching their kids learn.''

Brad and Angelina - who have four other children, Maddox, 12, Pax, eight, Zahara, seven, and six-year-old Shiloh - later enjoyed a romantic dinner at Hollywood's Roosevelt Hotel.

It was recently claimed the duo will marry in May after they told friends to keep the last week of the month free.

An insider said: ''Brad has asked those closest to him to make sure they're free the week after the Cannes Film Festival finishes on 26 May.

''Brad will be in Cannes with Angelina and the kids to promote 'World War Z'. He has also blocked out a couple of weeks in his work schedule after which has made his friends even more certain.''