There is no whining or any assignment of blame in the letter. It is a very cogently worded request to refrain from adapting a purpose-built app meant to drive engagement at all cost (Instagram) for kids under 13.

Of course there is a political play here: if this group gets Zuckerberg to back down and admit his product might not be good for people under 13, then an argument can be made against Instagram as a whole. Perhaps you disagree with that point?