Jo-Jo what you are noting is unfortuately prevalent everywhere, from the most modern Orthodox Shuls, to the most chareidi of Yeshivah or Chassidic minyanim. Children, in general, are being brought up without being taught simple good manners, with a sense of entitlement (like their parents before them). They run around in Shul, disturbing people who are davening, without any control. When an adult admonishes them, they make faces, speak disrespectfully, and go on with whatever they were doing. Had I done such things, my parents would have been embarrassed and taken appropriate steps to correct my behavior. But they never had to, because they taught me how to behave, and showed me by their own example of good behavior in or out of shul. that is not happening today, all too often. Although I do somewhat question the wisdom of bedavka going to sit down at a table clearly populated by 10-12 boys (was it a Bar-Mitzvah? were there any other seats available?), still, the boys were out of line to speak disrespectfully to you.
Sometimes I feel we should go over to the parents of such boys (though not at someone’s simcha), and mention to them very casually, what happened. They may be unaware (many parents make themselves “nisht vissendik” about these things.