The Britons arrested in Turkey on suspicion of trying to enter Syria are believed to be members of the same family from Rochdale.
Five adults, aged 21, 22, 22, 24 and 47, and four children, aged one, three, eight and 11, were detained at the Turkey/Syria border and will be deported back to the UK soon.
The family were taken to hospital for a medical and fingerprinting in Hatay, southern Turkey, after authorities foiled their alleged attempts to enter Syria illegally to join a militant group in Hatay and Gaziantep. They were stopped at Ogulpinar, a military outpost.
Greater Manchester Police said there was no evidence to suggest the family posed a threat to Rochdale but assistant chief constable Ian Wiggett was at a loss to explain why a family would want to travel to Syria.
"What is obviously concerning is why a family were seemingly attempting to take very young and vulnerable children into a war zone; such a volatile and dangerous environment is no place for them whatsoever," Wiggett said.
"One of our primary concerns is the safety and welfare of the young children and we are working with partners to ensure a full safeguarding strategy is in place upon their return to the UK.
"I would also like to take the opportunity to remind everyone of their responsibility to help us in our fight against extremism and prevent anyone thinking of travelling to Syria or other war zones from going."
The Foreign Office said it is in contact with the Turkish authorities to help the investigation.