(A further response to the comment I got on my last post asking about this.)
Jewish kids were common, in fact I live very close to one of the bigger synagogues in my area. As a kid, I was aware that Jews existed and that they didn’t believe in Jesus and that Jesus was one. I remember thinking that Jews were basically Presbyterians who didn’t believe in Jesus, while Catholics were something totally different and strange. We sung Christian, Jewish and Kwanzaa songs in our Holdiay program at school.
I never recall any non-Christian kid getting made fun of explicitly about their faith, though a girl did once tell a Jewish girl on the playground that she was going to hell. There weren’t any teachers around, but I’m pretty sure the teachers would have stopped that.
There was a girl from Iraq in my grade who wore a headscarf. I don’t recall her getting made fun of for it, though I can’t swear it didn’t happen. I assumed she wore it because she was from Iraq and that’s how people from the Middle East were always dressed in my textbook, much like how I would have thought nothing if a French girl wore a beret. In retrospect, she was probably Muslim. When I was a kid, Islam was mostly something I learned about in World Cultures class. I remember hearing that Muslims saw Christians as “people of the book” and respected them, so I recall thinking Muslims sounded pretty okay to me, but it never occurred to me that I knew one.
By the time I got to high school, my friend Adam had taken to announcing himself “Hi, I’m Adam, your big Jewish friend!” and there was an Arab student league in my high school that put out a flyer of suggestions for helping your friends celebrate Ramadan. As I went to mitvahs and sensed the warmth and solidarity that presbyterian kids just didn't feel, it became clear that being part of the minority was a big part of how these kids defined themselves. It helped them figure out who they were and to be honest, my high school self envied it, so much so that I went to a few services at the synagogue. But I didn’t fit in there either.
So no, I didn’t hear nearly as many jokes about Jews and Muslims, or even Mormons. Mostly, it was Catholics and other types of Protestants, particularly those in denominations assumed to be of a lower social class.
Maybe I’m wrong and as the commenter implies, I’m deluding myself. But that’s how I remember it.