The Dost test, which is the law in the US, is subjective, but it does discuss what you're trying to get at here. It's largely about context. A video of a little girl running around in a swimsuit is not cp if it comes off as a child playing. Even a nude child playing in pool is likely not cp. However Cuties is cp, despite the lack of nudity or actual sex acts, because it shows gratuitous closeups of crotch and ass as well as little girls simulating sex acts.

Taking non-sexual videos clips of children and editing them to make them appear highly sexual is technically manufacturing cp under US law.