HTML/CSS does not teach things like algorithms and data-structures, but it doesn't need to. It's complex enough that kids with an affinity for programming will find it stimulating, but not so complex that dumbo Timmy over there can't do at least something productive with it. And it straddles that line between nerdy-programming and design, so you can engage the creative kids as well.
Family member's been teaching HTML/CSS to 14-15 year olds, with good results. Like all class topics, the engagement-distribution is a bell curve. 10% is lost like a puppy at sea, 80% is following along with varying degrees of success, and 10% are absolutely doing amazing things and taking it way beyond the class contents.
One difference with the other type of kids-programming isn't that some robot scoots around the gym, but that at the end these kids are making goofy 90's websites, with bonker color-schemes and bouncing images. Parents and administration love the former. The latter only really clicks for parents with some familiarity in the domain.