Video report by ITV News Correspondent Ben Chapman
Fears are growing for a seven-year-old boy reported to be missing in Barcelona following the terror attacks that hit Spain.
It is thought Julian Alessandro Cadman has dual British-Australian nationality.
He was with his mother when they became separated, a post on social media said.
UK authorities are "urgently looking into" the reports a British child is missing, Prime Minister Theresa May has said.
His mother is among those injured in the terror attack and is in a stable condition in hospital - but Julian has yet to be located.
His family posted social media appeals on Facebook in a desperate bid to find him.
Tony Cadman posted a photograph of Julian on Facebook, and wrote: "My Grandson, Julian Alessandro Cadman is missing. Please like and share. We have found Jom (my daughter in law) and she is (in a) serious but stable condition in hospital.
"Julian is seven years old and was out with Jom when they were separated, due to the recent terrorist activity. Please share if you have family or friends in Barcelona."
Speaking about the victims of the Barcelona attack, Prime Minister Theresa May said: "Sadly I must tell you that we do believe that a number of British nationals were caught up in the attack, and we're urgently looking into reports of a child believed missing who is a British dual-national."
Mr Cadman's Facebook profile says he lives in Sydney and is from Gillingham, Dorset.
In the photograph, Julian is wearing a jumper which has a crest that says "Chiddingstone Nursery".
According to the Associated Press, Australia's Foreign Minister Julie Bishop told reporters: "We are concerned for one Australian who remains unaccounted for."