naïve: (of a person) natural and unaffected; innocent. [source: oxford languages]

naïve art: of or denoting art produced in a straightforward style that deliberately rejects sophisticated artistic techniques and has a bold directness resembling a child's work, typically in bright colors with little or no perspective. [source: oxford languages]

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Some links to good articles explaining naïve art:

https://www.tate.org.uk/art/art-terms/n/naive-art

https://bluethumb.com.au/blog/art-styles/what-is-naive-art/?srsltid=AfmBOopnQeLboJLMlm9ZR4_RGGMuioeA78BrO2SiZLf4pvrSRYcHqDHP