Gefilta: consider this statement. “these youngsters come in early to secure themselves good seats”; Is THAT proper derech eretz? Once they secure this seat and eat a fair share of food, is it not proper to offer the seat to someone else so that the next person can sit down like a mentch too, regardless of age? Perhaps the children dont do it because there are adults who ALSO come in early to secure a good seat and then proceed to sit for quite some time while others are forced to stand.
In ANY neighborhood, has anyone ever tried to ask the children to get up so that other people, younger and certainly older, can have a chance to sit down at the table too? The implication is that children should automatically be perfect tzadikim. Children have to be raised properly. They have to be taught that it is proper to share things, including seats at a kiddush, with other people. They have to be taught that it is considered derech eretz to give up a seat for an older person. Is it?