Neil Patrick Harris wishes his adorable twins a happy 6th birthday -- See the cute pics!

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.

WATCH: Neil Patrick Harris on the Key to a Successful Marriage

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

Kindergarten fits these two well. #firstdayofschool

A post shared by Neil Patrick Harris (@nph) on

"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."

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HOLLYWOOD, CA - FEBRUARY 22: Host Neil Patrick Harris speaks onstage during the 87th Annual Academy Awards at Dolby Theatre on February 22, 2015 in Hollywood, California. (Photo by Kevin Winter/Getty Images)
Host Neil Patrick Harris performs on stage for the 87th Oscars February 22, 2015 in Hollywood, California. AFP PHOTO / Robyn BECK (Photo credit should read ROBYN BECK/AFP/Getty Images)
Host Neil Patrick Harris performs on stage for the 87th Oscars February 22, 2015 in Hollywood, California. AFP PHOTO / Robyn BECK (Photo credit should read ROBYN BECK/AFP/Getty Images)
HOLLYWOOD, CA - FEBRUARY 22: Host Neil Patrick Harris performs onstage during the 87th Annual Academy Awards at Dolby Theatre on February 22, 2015 in Hollywood, California. (Photo by Kevin Winter/Getty Images)
HOLLYWOOD, CA - FEBRUARY 22: Host Neil Patrick Harris performs onstage during the 87th Annual Academy Awards at Dolby Theatre on February 22, 2015 in Hollywood, California. (Photo by Kevin Winter/Getty Images)
HOLLYWOOD, CA - FEBRUARY 22: Host Neil Patrick Harris performs onstage during the 87th Annual Academy Awards at Dolby Theatre on February 22, 2015 in Hollywood, California. (Photo by Kevin Winter/Getty Images)
HOLLYWOOD, CA - FEBRUARY 22: Actor Neil Patrick Harris attends the 87th Annual Academy Awards held at Hollywood & Highland Center on February 22, 2015 in Hollywood, California.(Photo by Jeffrey Mayer/WireImage)
HOLLYWOOD, CA - FEBRUARY 22: Host Neil Patrick Harris performs onstage during the 87th Annual Academy Awards at Dolby Theatre on February 22, 2015 in Hollywood, California. (Photo by Kevin Winter/Getty Images)
Host Neil Patrick Harris performs on stage with actress Anna Kendrick for the 87th Oscars February 22, 2015 in Hollywood, California. AFP PHOTO / Robyn BECK (Photo credit should read ROBYN BECK/AFP/Getty Images)
HOLLYWOOD, CA - FEBRUARY 22: Host Neil Patrick Harris (R) and actor David Burtka attend the 87th Annual Academy Awards at Hollywood & Highland Center on February 22, 2015 in Hollywood, California. (Photo by Christopher Polk/Getty Images)
HOLLYWOOD, CA - FEBRUARY 22: Host Neil Patrick Harris attends the 87th Annual Academy Awards at Hollywood & Highland Center on February 22, 2015 in Hollywood, California. (Photo by David McNew/Getty Images)
Neil Patrick Harris (R) and his husband David Burtka arrive on the red carpet for the 87th Oscars February 22nd, 2015 in Hollywood, California. AFP PHOTO / MLADEN ANTONOV (Photo credit should read MLADEN ANTONOV/AFP/Getty Images)
HOLLYWOOD, CA - FEBRUARY 22: Host Neil Patrick Harris (R) and David Burtka attend the 87th Annual Academy Awards at Hollywood & Highland Center on February 22, 2015 in Hollywood, California. (Photo by Michael Buckner/WireImage)
Neil Patrick Harris(R) and David Burtka arrive on the red carpet for the 87th Oscars on February 22, 2015 in Hollywood, California. AFP PHOTO / VALERIE MACON (Photo credit should read VALERIE MACON/AFP/Getty Images)
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See more adorable celeb kid back-to-school pics in the video below!

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