I'm in the US and my DCs all went to school here.
Exchanging non-romantic Valentines was a thing all through elementary school from age 4 on. The idea came as quite a shock to me when I first encountered it - we never did anything like that in my very jolly hockey sticks primary school in Ireland, where any kind of soppiness or sentimentality was actively discouraged. But it wasn't what I initially thought it was.
The way it worked was that each child brought a card for everyone else in the class, with "From your friend "Child Name"" written on it, but no recipient name.
Back when my kids were in school, you could tape a lollipop or other wrapped candy to your cards. The food police have stamped that out in their old school, I hear, and the kids can now only attach pencils or other boring items. Quite a lot of schools now frown on candy and obv there can be issues with tree nuts and peanuts with some items, so maybe that's for the best, all told.
In the week before Valentine's Day, I remember my DCs decorating brown paper lunchbags (a little wider than airplane sick bags) for their classmates to drop their Valentines into.
You can buy little packs of cards for about $2.99 in supermarkets, dollar stores, etc. The packets have different themes - My Little Pony, Disney movie/ characters, Paw Patrol, Winnie the Pooh, and lots more, suitable for all ages. Some kids make little cards.
The rule is that you give a Valentine to everyone or no-one, no picking and choosing recipients. Even if you don't give any cards, you will still get some.
It was all very sweet, well organised, and simply a gesture of friendship.
High school Valentines were more on romantic lines.
It's quite disturbing that the parents of the class the OP described thought romantic or boy/ girl Valentines were an appropriate way to mark the day. What is wrong with people?