Blue, how will you turn 10?

A little dog named Blue is turning the big one-oh next month -- that’s 70 in canine years -- and she’s got quite a present coming to her.

Nickelodeon marks the 10th anniversary of the groundbreaking preschool show “Blue’s Clues” with the prime-time special “Meet Blue’s Baby Brother,” airing at 8 p.m. Sunday.

That’s right: Blue, who we always figured to be an only pup, has a long-lost sibling.

Viewers will have to sit in their thinking chairs, take out their handy-dandy notebooks and travel through the world of Puppyville to find the canine cohort. And instead of searching for the blue paw prints, as is the norm for the show, “we go through a journey playing the very important game of Gold Clues because it’s a very big deal,” said “Blue’s Clues” co-creator Angela C. Santomero.

The idea of adding a sibling came “from the preschoolers themselves,” Santomero said. “One of the things that is a huge milestone in their lives is when they get a baby sister or baby brother.”

Since the September 1996 premiere of “Blue’s Clues,” the show’s creators have made it a policy to cull new story lines from kids’ minds. Brown Johnson, Nickelodeon’s executive creative director, thinks that’s precisely the reason the show has remained popular among viewers, critics and educational groups alike.

“I think the secret sauce of ‘Blue’s Clues’ is basically the opinion of people under 5,” Johnson said.

After a few misfires -- Blue started off as an orange cat, and the French-accented Mr. Salt originally sported a Brooklyn brogue -- the show’s creative team came up with a first-of-its-kind program in which the characters talked to those who tuned in, asking questions and seeking help to solve a mystery.

Parents who saw the show during its development were perplexed about the trademark pauses that occur when the host asks a question and waits quietly for an answer from the TV audience.

“Parents were like, ‘This is too slow. My kid will never watch this,’ ” Johnson said. “Meanwhile, in the next room, their child was shouting and pointing at the television.”

Sunday’s hourlong special combines the animated world of “Blue’s Clues” with the puppetry of “Blue’s Room,” a version of the show that has aired on Nickelodeon as a series of specials. The network is scheduled to launch “Blue’s Room” as its own series in January. (The original “Blue’s Clues” series ceased production in 2004 but lives on in repeats, where it consistently ranks among the top five commercial shows among preschoolers.)

Less than a year after its premiere, “Blue’s Clues” won a Parents’ Choice Award, which recognizes the best in children’s media, and in 2002 it scored a coveted Peabody Award for general broadcast excellence. The series’ format has been mimicked by shows such as “Dora the Explorer,” “JoJo’s Circus” and “Bear in the Big Blue House.”

“ ‘Blue’s Clues’ completely broke the mold, and I’m not sure we can ever do that again,” Johnson said.