Alyson Hannigan: Neil Patrick Harris "So in Love" With Newborn Twins!

Neil Patrick Harris and partner David Burtka doubled the size of their family last Tuesday, when twins Gideon Scott and Harper Grace were born via surrogate.

Harris' How I Met Your Mother costar Alyson Hannigan tells UsMagazine.com the brand-new, first-time dads are over the moon.

"I saw them this morning," Hannigan, 36, told Us of the couple at Elle's 17th Annual Women in Hollywood event Monday. "They are just so happy and just so in love with their babies!"

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Actor Harris, 37, announced the joyful news on Friday via Twitter, writing: "Babies!...All of us are happy, healthy, tired, and a little pukey."

Hannigan hasn't yet met the couple's new son and daughter, but got a glimpse with "a lot of pictures," she told Us.

The actress added that she "absolutely" already sees a change in Harris since he's become a parent. "It's just really cool."

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She got a sense of her pal's paternal instincts with Satyana, her 18-month-old daughter with husband Alexis Denisof. What kind of dad will he be? "He is going to be great! If he is anything like he is with my baby, he is going to be fabulous."

Back in August, Emmy winner Harris told Ryan Seacrest he was "trying to read as much as I can" before the twins' arrival. "There's only so much you can do because each baby is super individual and totally their own person ... [I'm] very, very excited."

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This makes Harris the third HIMYM castmate (out of five actors) to enter parenthood. (Colbie Smulders and boyfriend Taran Killam welcomed daughter Shaelyn in May 2009.) "We are all so excited," Hannigan gushed. "Three of the five have babies so we can dominate [with] baby talk!"