I wonder if there is an adjective to describe orthography that deliberately aims for the kind of irregularity or defects one might find in a young child, but is an obvious and deliberate style, rather than an attempt to fake a child’s handwriting. The Spanish artist Joan Miró came to mind, but on checking his signature it isn’t quite what I thought. Anyway, the question was actually provoked by the derivative design on a bottle of chianti (shown below).
“Faux-infantile” is the best I can come up with myself. “Naïve” might fit the design.