(I'm sorry, I would link to the picture I'm talking about, but I currently have neither access to the picture nor a scanner, and I can't find the picture online...)
My grandmother owns a children's encyclopedia from the 1930s called the Wonderland of Knowledge, and in one article there is a picture of a young white boy, aged 10 at most, wearing a ring. The article is about dental care as opposed to something about 'exotic peoples of foreign climes', and the article has absolutely nothing to do with jewellery whatsoever. The boy looks like he's from a fairly middle-class/well-off background.
So was it common for boys in those days to wear jewellery like that? I dunno, it's just that boys wearing rings is not something I associate with the 1930s...
According to Emily Post (Etiquette for the time), it is suitable for a gentleman to wear a ring besides a wedding ring, cufflinks, a tie clip or tie tack, and a simple chain or fob on a pocket watch, or to wear a wristwatch.
Most boys wouldn't because their families could not afford jewelry, least of all for children who might lose or damage it, and then it would go to girls before boys. But an upper-middle-class/lower-upper-class boy might have one without exciting comment.
Remember, people often dress up their children in their best for photo portraits. So this is probably not what he plays sandlot baseball in.
But children then did "dress" more. A suit and tie was ordinary school wear by the teens.