So yes, parents are a cause of a lot of kids' anxiety. But biology also puts a lot more kids at risk at it through no fault of their parents.

What kinds of things do parents do to cause more anxiety in kids?
Overprotect in the real world instead of letting kids engage in light risky play/behavior;
underprotect in the virtual world where they get taken advantage by apps designed to play with their anxious systems (See Jonathan Haidt);
Be overly anxious ourselves, especially about them. That anxiety rubs off on them. They observe and notice.
Lack of emotional connection with children
Harsh parenting
Too much criticism ... or praise! (see Carol Dweck's work)
Transmitting irrational fears to our children about the world, society, their lives, etc. (liberals unfortunately do this quite a bit as they are anxious about the world themselves).