Age 7-8 are in 'junior' school? In America what grade does that translate to? In the US, kids 7 or 8 years old would probably be in the third year of school.

In Alaska, and for that matter, west coast schools, group outings for 15-20 youngsters might entail perhaps four adults. BUT, that might be totally dependent on the activity when they arrive at their destination.

Besides which - in a group of 15-20 kids- was there any way to tell if the children were troubled or delinquent in some manner? Some situations demand almost one to one supervision.