Being on a security camera is very different from covertly photographing a kid from only a foot or two away. Why make such specious comparisons?

It's not the case when you're inside Costco. I'd also argue that it's not open to the public because you're required to have a membership to go in.

The point is, Costco is taking many pictures of you, including possibly correlating with events or actions.

We accept Costco taking pictures of you as a condition of entering the store and securing a membership.

The same does not go for random creeps wanting to take close up pictures of a child.

In this specific example, sure. You have no expectation of privacy in public and you are photographed, repeatedly.

The creep behavior is the problem. The photograph is a symptom of it.

It may not be illegal in the US, but I wouldn't call it silly to not want strangers to take photos of you and your kid in public.