Would you thought of these children as 'beachballs' had they been well-behaved and not rowdy at all? You draw yourself to something negative, the screaming, and make a judgement that they are also overweight. This comes down to parenting too. In public there are 3 kinds of children generally: Those who know how to behave, are polite, and can have a good time without being abnoxious; those who are cranky, usually smaller children, who cry or whine due to being tired or hungry; and those who are completely out on control. Most parents who are attentive enough for healthier diets would have socially polite and respectful children, and the usual you would see is the rowdy, uncontrolled children are more likely to be a bit overweight. These 'beachballs' are children and while you may look at them and think they are gross, think its a better idea to look at their parents and most likely you will see these out of control overweight children accompanied by a stressed out exhausted looking parent or one completely ignoring their behavior.
As far as social development. I find making sure they have the skills to make friends important, but popularity not as much. Ideally a popular child who is popular due to their personality and getting along great with other children would work out greatly. On anotherside trying to make them change their personality or the way they prefer to be in order to be accepted by large groups would probably do more harm than good. A couple good friends while being able to maintain being yourself is much better than a bunch of friends you have to put on an act for them to like you.