Re. Camp Bestival, are you planning on arriving early the first day (Thursday)?
I'd have a think about how early you can bear to arrive. I steward at various fests including Glastonbury, Reading and Bestival (Camp B is one we do too) and based on those, customers are very committed to getting into the site asap 
Weekend camping tickets for Camp Bestival have sold out in recent years.
Imo a lot of people at Camp B will have giant sized tents, gazebos and paraphernalia (DIY glamping
) which will cause campsites to fill quickly. People also save space for friends...If you arrive late be prepared to be stuck in the most far flung field, miles from the festival/ car park/ toilets
Having said that I don't know the site (maybe it's more compact than I'm used to - if so ignore my scaremongering
). Try and find a Camp B veteran between now and July to clarify 
Be prepared to queue on foot avec luggage to get in, depending on time of day
It can be rather tedious after the excitement of arriving!
Most festivals don't allow glass so you need to decant your alcohol and condiments into plastic bottles/ containers prior to leaving, or have it confiscated at the gate
Wine boxes, cider boxes, G+T in cans, spirits decanted into plastic bottles/ hipflasks are the way forward 
A collapsible handtruck or folding wheelbarrow, plus bungee cords (poundshop), can be very useful if you have a lot of gear to transport from car to pitch. Basically look for something with big wheels. Tiny wheels are absolutely useless in the mud/ over distance e.g. trolley suitcases. I'm fairly certain once you're wristbanded you can make return trips to the car to collect further kit. Take the tent and other essential things on your first trip and send DH/ older kids back for the rest once the tent is up and you're enjoying a nice
or
!
Alternatively there are such things as festival taxis (aka golf buggies) which are available to hire at the gates. They transport you and your gear into the campsite! They're active on the departure day too. Not cheap but might be worth it. Some festivals let your hire wheelbarrows too. Check the FAQs.
Camp Bestival offer something called Camping Plus whereby they save you a pitch in a special area (check dimensions against your tent, looks like 5x7m) for £125 
You will have a great time! My friends say the fireworks over the castle are spectacular 