Campers joined police to search through the night for the missing boy, who was last seen at a campsite at Thistledown Farm in Nympsfield, near Stroud at around 7pm last night.
Police said a more extensive hunt was due to start as daylight breaks.
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Only handful of beaches have RNLI lifeguard cover during school holidays - the Maritime and Coastguard Agency warns.
Our Devon correspondent Seth Conway has been talking to a family who say without the hospitals, their children may not have survived.
It's going to be a windy one tonight and into the weekend - it could even touch gale force along the south coast.