Can a underage kid travel with an expired passport?

Yes mine have in the past by mistake!, with a lot of persuasion but at the discretion of airline. If you take child abroad and manage to leave UK then it is up to the customs at the destination to allow entry. If you are refused entry You will be responsible for all costs/flights if deported!It is a huge gamble and has become very much more difficult in recent years to "talk" ones way out of this v common problem! Why cant passport office send a reminder like tax disc when passport is about to expire?