It's in Chapter G of the staff travel manual.
Basically, as your kids are between 5 & 12 years old, they can travel as UMs provided any transit stop will not exceed 4 hours... if it does then you will need to arrange for someone to collect & care for them on the stop. If not then tickets will not be given- same goes for where they have to transfer between airports.
They can only travel as UM on confirmed tickets (i.e. to fly STBY they have to be with grandma)
Between 12 & 15 they can travel as Young Person (less supervision than UM but still some checks in place the difference being they can travel subload (apparently)
Hope this helps...