Often children see things just as clearly as adults but tend to say what they see without filtering their thoughts.
"Grandma's a bit grumpy today". Everybody agrees, but hesitates to say so.
Naïve art aims to be as honest as that. It is childlike rather than childish. It has a charm and a directness which engages the viewer on the most basic level. It is not the poor efforts of the untalented. Henri Rousseau and Vasily Kandinsky both painted in a naïve manner but are recognized as masters.
Any subject matter is possible. It's the clarity of childlike vision which makes it Naïve.
Grey day on beach ladies by the Pier
Teresa Tanner
Even portraits can be driven by the same simple honesty.
Thinking like a child can be very refreshing - but don't necessarily tell Granny she's grumpy.
Looking at an artist's childlike response, in paint, can be equally stimulating.