According to Insect Identification, a "child of the earth" insect is the English translation for a common Spanish name of the potato bug, "nino de la tierra." The Archnids E-Zine reports that in New Mexico, the term "child of the earth" is also applied to large arachnids called wind scorpions. The two groups are not related. Wind scorpions are closest to spiders, whereas potato bugs are a kind of wingless cricket.
Both creatures are found in the North American southwest, with the potato bug having a wider range encompassing the west coast, northern Mexico and the Pacific northwest. Wind scorpions prefer very arid conditions and are found in deserts from Arizona to Canada, although the Pacific coast is too humid for them.
Orkin notes that from the front, the potato bug's bulbous head looks like a tiny human face, which may be where the name "child of the earth" comes from. Arachnids E-Zine also notes the potato bug head's fanciful resemblance to a baby's head. How wind scorpions acquired the "child of the earth" name is unknown.
Neither creature is dangerous to humans, although potato bugs do bite. Both insects prey on pests. Potato bugs may damage gardens, as they are known to devour tubers.