The thing about brains, at least mammalian brains, is that for a species to be really smart, like primate, tool user, abstract reasoning level smart, it seems like they have to be born with pretty big brains already, close to the size and complexity they'll be as adults. I am not sure why this is, but it's a pattern we see, at least with mammals. Searching for papers about it brings up things like this
but glancing at it quickly, that one seems to be saying that humans evolved to be smart in order to take better care of human infants that are so very helpless at birth compared to foals that can walk within an hour after they're born, and so on. I am not sure how to interpret this. Maybe it's a primate thing. I know bears are pretty large and intelligent carnivores, and baby bears are really tiny hairless things the size of a potato. @Wallbeige
It's still going to be a bigger package than babby alone. If you believe Wackypedia the only extant egg-laying mammals are the monotremes
, and their relatives. They seem to be a rather primitive branch of mammals, with lots of distinctive anatomical weirdness going on, suggesting they evolved in isolation for tens of millions of years. They are sufficiently weird that I am not sure we can use them to make assumptions about egg-laying ponies.