They say kids grow up in the blink of an eye, and Neil Patrick Harris fans are just now realising how true that is as his twins celebrate a major milestone.The 53-year-old actor shares Harper and Gideon with his husband David Burtka, 51. The couple have been married for 12 years and welcomed twins in 2010.Time goes by so quickly and fans of the family are only just realising. To celebrate his kids’ sweet 16, Neil took to Instagram to share four pictures of the 16-year-old twins.“Harper and Gideon turned 16 today,” the proud dad gushed. Two of the snaps show the twins as babies while the other two photos are more recent snaps.“It’s amazing to see how they’ve grown and I couldn’t be prouder of the people they’ve become. Mostly, though, I’m so grateful that they can drive me around everywhere now.”

The How I Met Your Mother star, 53, also gave a special shoutout to his husband in the caption.The adorable tribute shows baby Harper wearing a pink tutu and holding a tiara, while Gideon was pictured smiling at the camera. The more recent pictures feature Harper modelling while Gideon sits on a boat wearing sunglasses.Fans wasted no time sharing birthday wishes in the comments, with many followers shocked by how quickly the twins have grown.“Wait what how old are we??” one shocked fan commented.Another follower wrote: “Wait… weren’t we just at the baby shower??!!”A third person quizzed: “I’m sorry HOW OLD?”Similarly, another fan said: “Sixteen? Already? I think we need a re-count! Pretty sure they can’t be more than five or six?”The twins were born via surrogate in October 2010 while How I Met Your Mother was still on the air.The actor shared an insight into life as a father of teens during a recent appearance on TODAY with Jenna & Sheinelle. He was joined by Julianne Hough and Austin Scott to discuss the new Broadway production of Damn Yankees.Jones said that his twins must think he’s cool, saying: “They know how cool you are, obviously, at this point.”But Neil said he doesn’t think so, stating: “Oh, I don’t think they think I’m cool at all. I’m one of their fathers.”