Ok, this is a list of Tom's Kit and stuff we shared I've not included my clothes as most of it is duplicated though in my size and not his. :)
Bike - Ragley Hardtail with 3*9 transmission, Reba air forks and a USE Vybe suspension seatpost. The seatpost makes a great lightweight alternative to a fully suspended rear end, and definitely saved his butt from some of the hammering. Mudhugger mudguards F+R. Exposure Toro MK6 front light and some unknown rear led light.
Luggage - Alpkit stem cell x 2, one for a water bottle, the other for quick access to his waterproof jacket. Custom two compartment Stingray frame bag which held some of our lightest bits and pieces. A kids bike is unlikely to have clearance for a seat mounted Koala I did have one on my bike though which carried the tent and some extra food.
Riding clothes - Rapha bib shorts. Synthetic long sleeve baselayer top. Rapha classic Jersey and arm warmers, Btwin long sleeve thermal windproof jacket. Rapha Rain Jacket. Decathlon waterproof trousers. Sealskinz knee length socks. Fingerless mitts and a pair of primaloft mittens. Pearl Izumi SPD shoes ( a size too large). Buff, Cotton cycling cap. Mens small armwarmers used as leg warmers.
Night clothes - Thermal top and bottom base layer. Decathlon fleece jumper. Mountain warehouse synthetic gilet (aged 7-8, sized to be a snug fit) Merino socks. Rapha Merino beanie.
Sleeping - Yeti 900+ down pied'elephant sleeping bag which fits him as a full length bag. 3/4 adult sleeping mat. Tent Alpkit Ordos 2
Night clothes and his sleeping kit all fitted into an 8 litre Alpkit drybag. Whilst I used the 13 litre version for my stuff.
Tom carried the SPOT tracker strapped to his bar bag. He was taught how to work it including how to use the SOS function.
He had his own mobile phone and knows how the 112 emergency system works.
He also carried a whistle to call me with a long blow, or to use the international SOS call.
He didn't have a GPS on his bike, but he knows how to use mine.
The only thing other than spares which we took that we didn't need, was a midge head net each.
This setup worked well for us. Though it was May the temperature with wind chill was often close to freezing. He'd wear similar clothing riding in the Peak District where we live in December.
One tip, is when you stop for the night is to make sure that your kid gets out of their damp cycling stuff, and into their dry evening clothes asap.
Likewise in the morning make sure that all they need to do is pull down the tent before putting on their cycling wear.