This article says that google photos’ model can still have trouble telling your pets apart if you have the same breed - it kind of disproves your point. The model needs to be explicitly told which cat is which. That said, I’m pretty sure a toddler would probably need to be told which is which too.
Don't forget humans don't just see pictures - they see a video upon which they are learning.
Micro-movements of cat body parts and their more general character traits could be the only hint that separates two supposedly same cats.