There is something to be said for personal responsibility, but there's definitely a risk with these things. Parents simply cannot be with their kids 100% of the time. Little kids are desperately attracted to shiny things and put them in their mouths. These little things are responsible for a lot of serious injury.

If there's a point in the film where the apes have access to helmets and protective body armor, but they're like, "Nope, we'll just stick with paint," then yes, it's a little silly, because that just makes them seem stupid and impractical. But the initial adoption of warpaint itself seems reasonable.

Why? Even Annalee wasn't completely sure whether the filmmakers were going for a Native American look or an African one. Because human societies all around the world have independently adopted these styles. But it's totally far-fetched that apes would do the same?

Agreed, look at most "primitive" civilizations around the world and there is a common use of war paint and feathers for display.

"Also, we never understand why a community of apes who were raised in high-tech city labs would start wearing feathers and warpaint...why would they suddenly adopt a neolithic Indian style of dress?"

I reject the idea of horse racing. The end.