I don't have a big problem with families that pre-board with very small children. However, I do think it has been abused. Once a child can walk and understand their parent(s), say around 2 years old, I think the need to pre-board is diminished. I have seen families with children that must have been at least 10 to 12 years old (my guess), that pre-boarded. Of course I know there is no way for United to actually know the age of the children since they don't need IDs domestically, but I have heard other airlines say "Anyone traveling with child under the age of 5 may pre-board".

What I would really prefer is if the families with small children would be the last to get off the plane. Sometimes the families get the bulkhead for their infants, so they are in front of the entire economy class. Then they stand in the aisles getting everything together to get off the plane while everyone is stuck behind them. When my child was very young, I always waited for everyone else to get off the plane first before stepping into the aisle.