'Bluey' fans worry the hit TV show is about to end. A lot of money's at stake — and there are challenges ahead.

"Bluey" ranked among the most-watched shows in America last year but it could suffer some growing pains, one expert says.

• "Bluey" fans are worried the series could end with its third-season finale on Sunday.
• The "Bluey" brand is worth an estimated $2 billion but faces some challenges going forward.
• The kids TV show ranked among the most-watched streaming series in America last year.

Fans of the children's TV sensation "Bluey" fear their favorite show will end with the third season's finale this Sunday. There's a lot of money at stake and if the series does continue, it faces challenges down the line.

Winning hearts

"Bluey" is an Australian preschool show that stars a family of Australian Cattle Dogs or "Blue Heelers": Bluey, her younger sister Bingo, and their parents, Bandit and Chilli.

The show has become wildly popular in the US. It ranked as the top children's show in the country last year, and the second-most streamed series after Suits, per Nielsen data.

It has taken off among viewers because it's funny, appeals widely, and tackles real issues that many families face. Episodes focus on how children learn about the world through play, and how parents can join in the fun and help their kids navigate challenges while also dealing with their own issues.

"Bluey is relatable to both parents and kids and uses humor and realistic situations in its storytelling," Yalda Uhls, the founder and CEO of the Center for Scholars & Storytellers at UCLA, told Business Insider.

"Sesame Street is similar in that parents don't mind watching that with young children."

The show's creator and writer is Joe Brumm, a father of two young girls. It's produced by Ludo Studio, its distributors include the commercial arm of Britain's BBC, and it's available on Disney Plus.

The latest episode centered on Bandit preparing Bluey and Bingo to move home, and concluded with the appearance of a foreboding "For Sale" sign on the lawn of their family home.

This weekend's season finale is titled "The Sign" and will be 28 minutes long, dwarfing the usual 7-minute episode length. The special's unusual size, game-changing subject matter, and the fact that a fourth season is yet to be announced have fueled concerns that this might be the show's end.

Making money and growing up

That's a big deal, not just for fans but also the business of "Bluey." One valuation expert told Bloomberg that the brand is worth an estimated $2 billion. Another source claimed Disney had explored acquiring the property.

Those behind "Bluey" have leveraged its immense popularity by licensing its characters. There's now endless amounts of merchandise — this father of a toddler already owns "Bluey" books and toys and has been eyeing a "Bluey"-themed doctor play set — if only he could trust the family dog not to chew the stethoscope.

If "Bluey" ceases playing on screens, a lot of money might be left on the table. Consider how Disney monetizes smash hits like "Frozen" by releasing sequels and spin-off TV shows, and by featuring characters like Elsa and Olaf across toys, books, clothing, video games, theme parks, cruises, and resorts.

But if "Bluey" lives on — which it almost certainly will in some form, given its huge popularity and relative youth as a franchise — it will have other hurdles to jump.

Capturing fresh viewers as existing ones move on is likely to be a big one.

"As with any show related to kids, the audience will grow up, and if it doesn't create storylines that hold the attention of a new audience, it may lose viewership," Uhls said.

The show's reliance on Brumm could also make it tricky to scale, and limit how much a buyer will pay for it. Too much success, too fast, might cause the show to lose its way too.

Whether Sunday's episode is a goodbye for now or a permanent send-off for "Bluey," it'll be interesting to see what happens next.