Which children's franchise is the biggest theme park draw?

I am almost sure, although sad to say that it is Minions. I would rather it any of the other options (oh, how I wish people talked more about Peanuts nowadays), but it is what it is.

(now, a kids franchise I would love to have a ride dedicated to, but I don't see that happening anytime soon would be Captain Underpants... TRA LA LA LALA!)

Lego outdraws all the other non-Disney kid-centric IPs- half the reason Merlin Entertainments draws 64 million guests a year making them the official world's second-largest operator of theme parks and attractions when measured by attendance. That said, Peppa Pig is way bigger with kids these days than most of the other options- and is also in Merlin's hands for the theme parks and attractions industry. Sorry to say the Looney Tunes, Hanna Barbera and Peanuts characters don't tend to be big with the small kids set these days- though Snoopy is bigger in Japan than elsewhere, much to Universal Studios Japan's benefit:)

We live close to Sesame Place, so my boys lived and breathed the franchise. My younger son was so in to Elmo.

For my son it would be Lego top and then probably Minions. Not sure he is into any of the others really.

What about SpongeBob Square Pants at Universal Studios?

I think kids really, really love SpongeBob, although he and his friend Patrick are pretty much only walk-around characters at the park, with no attractions or food or merchandise tie-ins.

Sesame Street has stood the test of time, but loses its appeal for kids once they pass Kindergarten. LEGO has proven itself to have multi-generational appeal with enough franchises (Ninjago, Batman, Duplo) to have something for everybody.

Lego wins here by a large margin, especially if the Lego versions of other IP are considered. Even without those, it has by far the widest range of offerings, and is also the easiest to adapt to interactive, immersive theme park attractions. As for the others...

-Minions is probably currently in second place, but I'd say this is the one with the least staying power
-Sesame Street is timeless, but skews a bit too young to make a land appealing to kids much above first grade
-Looney Tunes is definitely a compelling property, but I worry that the sensitivity of today's culture may limit exposure of that brand to modern children
-Dr. Seuss is timeless, but doesn't translate well to the theme park environment
-Peanuts is last...it just isn't popular with children today and I doubt most know of it beyond what is present in the Cedar Fair parks

Truthfully, the best children's franchises after Lego would probably be something based on Nickelodeon or Cartoon Network shows rather than anything on this list, hence why those are seeing more investment (such as the new Nickelodeon Universe park in New Jersey) than anything listed here. Of course, once Nintendo is in the market all of this will be a moot point, but that's still several years away.

Depends, what are the youtubers telling kids to like?
Because that's what will be popular.

PinkFong and baby shark would get my vote ..... LOL .... :)
Yes, I know it's not at any parks .... yet !?!?

Thomas the tank engine should be included, as it's at Drayton Manor Park.

And let's not forget Angry Bird land at Thorpe Park.

Lego is foremost an amazing toy concept. Minions are characters. I think kids like both a ton. Never thought little girls would go wild about Minions but they sure do.
Sesame Street will probably hit high with toddlers and pre-schoolers.

Has to be Lego, those are huge deals for kids of all ages and the success of Legoland proves it.

AJ - I'm curious to know why you feel that way about how well Seuss lends itself to the Theme Park environment.
Perhaps I'm biased, but I think IOA's Seuss Landing is one of the best themed lands focused on younger guests and those looking for nostalgia.
Seuss' style is pretty perfectly presented and Easter Eggs (green and otherwise) abound to the sharp observer.
Even before the Wizarding Worlds brought us Butter Beer and Wands, Seuss Landing offered Green Eggs & Ham, Moose Juice and red and white striped hats like the cat himself wears to eat and buy. In lots of ways it set the course for how well F&B and Merch from the IP could be brought to life in the park environment.
One initial draw back was how the Seuss estate was hesitant to have its work turned into an in park environment. Just as Seuss Landing set the course for F&B and Merch, the way UO learned to court Mrs. Giesel had to inform them on how to approach JK.
I think the biggest drawback is how long it took to get the attraction that is now known as Sylvester McMonkey McBean's High in the sky Seuss Trolly train ride open. That was a huge bummer for the first several years the park was open that something that looked like a ride, wasn't yet available to guests.
The other is the fact that there has been no major addition to the land. I think we are all hoping someday to get a coaster-like ride down the summit of Mt. Crumpet with The Grinch.
Other than that, I'm curious to know what your thoughts are on why it's not a successful IP for parks.

OT, while Lego toys are their original source, this intellectual property has expanded into a wide variety of characters and those are what these children embrace at the LEGOLAND theme parks and Discovery Centers. Block Lives Matter!

I debated between Lego and Minions before voting, but went with Lego because, other than one major attraction at Universal, I don't see a lot of Minions in the parks. Lego has entire parks devoted to their product, so you go there if you love Lego, and don't go their if you don't like Lego.

OK, Robert,
you actually mean "... to a theme park in the USA ?"
Which was not stated/written explicitely in your post.

Here, In Belgium, none of the choices you propose are valid. Not in the slightest way.
Here, when it's about childeren's aimed IP rights on TV & film, the exclusive answer would be :
Studio 100
Their actors performed and animation brands, stand out at the (commercial) top. Add on: their life performances...
Even more :
Studio 100 performs OVER Disney, here !!

I would assume Lego hands down - but I’m curious about the ratio of boys vs. girls who choose Lego. Something like Harry Potter attracts both genders - is Lego as interesting to girls as it is to boys?

Rob, it's less about Dr. Seuss not working in a theme park and more about it not fitting the current mold of themed areas at destination parks. Many of the Dr. Seuss stories could be made into a solid attraction, but in most cases it would be challenging to expand the material beyond what is present in the story and into a whole immersive world with new narrative possibilities. Granted, there are a few stories (most notably The Grinch) that lend themselves to this, but it would be incredibly challenging to create something like "Cat in the Hat World" that would be compelling in a theme park. Seuss Landing worked in a time where lands weren't fully immersive journeys into a single IP, but its design is outdated and the lack of crowds there shows that (it was consistently the least busy area of IOA on my visit in 2017). Creating something new with the same design philosophy...I'm not sure how successful that would actually be (especially without a movie attached to it).

AJ - Respect. I am perhaps behind the curve here, but I still believe there is room in the Theme Park-scape for lands based within a loose idea such as "Adventure" or "Frontier" or "Fantasy". Granted, those are all obviously from Disney castle parks, but they most easily support my thought.
I also feel like we as deeply involved fans expect more that what the majority of the ticket buying, turnstile spinning pubic is looking for, especially kids at the One Fish, Two Fish reading level.
I am also a desperate hold out for original attractions NOT based on existing IP. Many if not most of Disney's classic attractions were not based on anything other than a great original idea. I really hope are not done with that. I understand the economics behind it, and it is understandable. Heck - look at Broadway. There are precious few big musicals on the boards that are not based on something the public is already familiar with. *Come From Away* and *Dear Even Hanson* are all that I can quickly think of off the top of my head. Why risk all that money hoping to capture the imagination and dollars of the public, when a tried and true story brings you a built in audience - *Mean Girls*.

Anyway - thanks for the response. I think it will be a lot of fun to see where we are in the next 15 or 30 years and if this current trend continues. Nothing new and exciting stays that way for long. Behind the scenes movie making magic themes were all the rage only 30 years ago and now most of the attractions that the Disney Hollywood Studios and Universal Florida opened with have been replaced with this current mode.
Ain't it wonderful and exciting to watch?

Rob, I prefer theme parks produce attractions based on original intellectual properties too- themed entertainment is essentially a story telling medium. Sadly, the industry has an addiction to established, global intellectual properties. That said, there are still theme parks that succeed today with attractions based on their own, original IPs, Efteling remaining the gold standard for this.