Please note that most Join MEets are a collective effort, organised by a loosely associated group of people who neither form nor represent any kind of "official organisation".
As a group we usually try to make every effort to make meets family-friendly — a huge number of Joinees are young people, and also there are many entire families who have gotten involved together.
However, nobody will be "in loco parentis" of unaccompanied children, so parents should consider coming along with their children. It's particularly important to state that after the day's fun in the streets of a city (or wherever else), we will often finish up in a pub or a function room at a pub, and obviously, those under the legal age will not be able to stay after that point; note that the legal age may be lower than 18 for those still accompanied by a parent.
At meets, people often stay overnight in hostels, hotels, and on the floors and couches of local Joinees. Children are asked not to stay overnight without their parents. Permission is not enough — we ask that a parent (or other suitable adult) accompany you, because none of us will be able to accept responsibility to be your "responsible adult". Please note also that this person will need to stay reasonably sober, as the law would expect of a person in a position of such responsibility.
We're very sorry about this restriction, but we know you will understand that this is for everyone's safety and enjoyment of meets.