Paintings of this kind typically have a flat rendering style with a rudimentary expression of perspective. When this aesthetic is emulated by a trained artist, the result is sometimes called primitivism, pseudo-naïve art, or faux naïve art.
One particularly influential painter of “naïve art” was Henri Rousseau (1844-1910), a French Post-Impressionist who was discovered by Pablo Picasso.
Simplicity rather than subtlety are all supposed markers of naïve art. It has, however, become such a popular and recognizable style that many examples could be called pseudo-naïve.