I think the craziest one I’ve heard at my local zoo was calling a Eastern Black and White Colobus a “baby gorilla.” I can’t wrap my head around how that person thinks gorillas work.
I’ve also heard people misidentify tawny frogmouths as owls, scarlet ibises as flamingos, and African painted dogs as hyenas. These wouldn’t be too bad, and pretty understandable mixups for people who aren’t very knowledgable about animals, except all of those instances were right next to signs saying that animals aren’t what they were misidentified as.
My local zoo also has both a dwarf crocodile and pygmy hippos, and if I had a dollar for each time someone said “Look at the baby crocodile/hippo!” I’d be rich.
All of these were from adults, but I don’t really hold it against kids when they mix them up. They’re still learning, and it’s kinda cute seeing them try to figure out what an animal is with their limited vocabulary. I think the best I’ve heard from a kid was calling a crowned lemur a “fox monkey”.