Fifteen children as young as 12 and six adults were found inside a refrigerated lorry entering the UK, it is understood.
Thought to be from Vietnam, the group were found concealed in a shipment of sparkling water at the Port of Newhaven in Sussex on Thursday.
The children were cold but are said to have not needed medical treatment and have been taken into the care of social services.
The lorry was stopped on its arrival from the French port of Dieppe.
A Romanian man, believed to be the driver, was arrested and charged with assisting unlawful entry into the UK.
Andrut Mihai Duma, 29, is being held in custody until a hearing at Lewes Crown Court on November 26.
A man aged 18 and a woman aged 27 have been removed from the UK, while the remaining four - a woman and three men - are at immigration detention centres.