Their whines are loud, annoying and unhuman. They are nicknamed "pea gas leakage" by the child-hating community, and it is often considered the most annoying sound on the planet.
If you define "intelligence" as the capacity to learn, babies are not stupid by any means; babies' brains have a far higher degree of neuroplasticity than adults'. That's why, for example, children can learn new languages much more easily than adults can. So really adults are the stupid ones!
Babies poop a lot and it's the icky kind of poop that looks like a jar of peanut butter fell into a tar truck that was vomited out of an orangutan's butt.
people that have babies tend to have a lower IQ, because people with a higher IQ tend to go for their jobs and studies- not for creating offspring. Making every generation, thus babies, dumber.