Really glad I can help!
Not sure of the deadline but as early as possible will obviously help. They will take entries in the week leading up to the event but strictly no entries on the day is the main rule. It will be about £14 per child for info.
It is strict about no parents/teachers in the hall and this is standard across all junior chess events that I have been to. It is just not practical to allow anyone except the arbiters in as there are always loads of questions and disputes to deal with especially with the inexperienced children. I have a son who has played for three years and before I started helping would spend the whole time he was playing looking through the windows of the hall to catch as much of a view of the board as possible or even just to see his mood. Now I help in the hall I stay away from his game because it is too nerve racking for me and too distracting for him.
At Downlands there are three separate halls used, one for the under sevens (joint boys and girls event), one for under eights-nines and tens (six separate sections 3xboys and 3xgirls in the different age ranges) and the under elevens and above in the upstairs hall with various different sections dependant on entries.
From experience I would advise the following for children at the first event
Get there early as parking will be limited as there is building work at the school
Get the children to play as slowly as possible, 25 minutes each is a huge amount of time for the primary school children and so many play the first move they see where even 20 seconds of thinking time would show them a better move. The controllers always advise this but so many ignore that if you can drill that into them they will have a definite advantage.
Teach the younger ones how to checkmate as I see so many positions where one child has massive material advantage but hasn't any idea how to finish it off. This is easier said than done! And try and ensure they understand stalemate,