Four children endured several hours locked in a refrigerated lorry in a failed attempt to smuggle them into Britain, the UK Border Force said.
The youngsters, aged nine to 16, were found in Dunkirk in France the back of a chilled trailer used for transporting soft cheese.
They had suffered temperatures of minus 2C (28F) and were taken to hospital suffering from hypothermia.
The children were among a group of four Afghans and three Iranians who were found last Friday in a Slovakian-registered lorry.
It was due to travel via Dover to Milton Keynes - leaving the stowaways in the trailer for another seven hours if they had not been found.
Paul Morgan from UKBF said: "This incident shows the desperate lengths that people will go to in their attempts to reach the UK.
"It also shows the complete disregard for safety and wellbeing shown by the people-smugglers who no doubt helped get them into this lorry.
"The group had already spent several hours in sub-zero conditions when Border Force officers discovered them. They had no way of getting out.
"If the lorry had carried on unchecked then this could have had fatal consequences, especially for the children."
The four children and one adult were taken to hospital and later given the all-clear. The group is being dealt with by French authorities.
The Bulgarian driver of the lorry was questioned by police and released without charge.