Neil Patrick Harris Wishes His Adorable Twins a Happy 6th Birthday -- See the Cute Pics!

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Neil Patrick Harris and David Burtka have the cutest children EVER.

Neil Patrick Harris and husband David Burtka couldn't be prouder of their twins, Gideon and Harper.

The two both took to Instagram to wish their kids a happy sixth birthday, sharing adorable pics of the stylish brother-and-sister duo.

"Gideon and Harper turn 6 today!" Harris wrote on Wednesday alongside snaps of the two going down a water slide. "Happy birthday to these big, bold, brave, bright, beautiful bundles of bountiful blessings. Boom. #balliteration @dbelicious and I love you kids SO much! #grateful."

WATCH: Neil Patrick Harris, Nick Lachey, and 6 More Super Adorable Celeb Kid Back-to-School Pics!

Burtka took to Instagram a day later to also gush about their twins.

"Happy Birthday to the most loving, fearless and most adventurous eaters I know!!" Burtka wrote. "@nph And I love you Gideon and Harper!"

Harris and 41-year-old Burtka married in Italy in September 2014. They welcomed their twins in October 2010 via a surrogate mother.

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Last month, Gideon and Harper celebrated another important milestone -- their first day of kindergarten.

"So many feels: excited, nervous, giddy, wistful," Harris, 43, tweeted about the big moment. "But mostly proud. Can't wait to see who they become."

See more adorable celeb kid back-to-school pics in the video below!