Neil Patrick Harris and David Burtka's twins, Gideon and Harper, celebrated their fourth birthday together with their celebrity dads over the weekend, Us Weekly reported.

The 41-year-old "Gone Girl" star and his 39-year-old celebrity chef husband took to Twitter Sunday, Oct.  12, to share the happy news with their followers.

"Happy 4th birthday, Gideon and Harper. I can't believe that you used to be tiny baby things. And now, this," Harris tweeted, along with a snap of the twins looking beyond excited Sunday morning as they prepared to open their birthday presents.

Burtka, who appeared in seven episodes of "How I Met Your Mother" as Sccoter, also greeted his twins on the microblogging site, along with an adorable photo of the two sitting on their front porch stairs. "Today is an exciting day!! Our twins turn 4!  I can not believe how old they are!  #solucky #happybirthday!" he captioned the photograph.

In August 2010, Harris announced that he and Burtka were expecting twins via a surrogate mother. And in October that year, the couple welcomed Gideon and Harper, People reported.

Harris and Burtka tied the knot during the first weekend of September this year. And talking on "The View" after the event, Harris explained that he and Burtka wanted to marry for the sake of their children.

"We just have been together over 10 years and I think when our kids got to the age where they were having reasonable conversation, when they're asking lots of why questions, to have a real clear-cut explanation of who their daddy is. I think it's great [to say], 'He's my husband' and it was easier than partner or boyfriend or something like that," explained Harris, as quoted by EntertainmentWise.

As for how private their Italian wedding ceremony was, the Golden Globe-nominated actor said, "It was nice. It was very small, intimate. Only 45 people were there. We did a destination wedding so it kind of kept the numbers down. I just wanted to be able to say nice things about David, to David, in front of the people who matter most to us...a declaration to share in front of our kids," according to E! News.