A gangmaster is believed to be behind the "exploitation" of seven Romanian children found working in a field.
The Gangmasters Licensing Authority (GLA) and West Mercia Police found the children with a group of adults picking spring onions in the Malvern Hills district on Wednesday.
GLA chairman Paul Whitehouse said the working conditions were "appalling".
West Midlands Police said they were "working with the GLA to try and identify one suspect in the case".
The GLA said a gangmaster was believed to have been involved.
Some of the seven children, aged between nine and 16, were with their parents and some were working alone.
Six of them were taken into police protection.
West Mercia Police said the families were living in the West Midlands and the children were initially placed in the care of Sandwell Borough Council.
A council spokeswoman said the police protection order was in place for 72 hours, but the children were now back in the care of their parents.
A child protection investigation will now take place, she added.
Mr Whitehouse said: "We discovered the children working, some of them with their parents but others without, and in conditions which, for the adults alone, were appalling.
"No proper clothing, no water, no appropriate lavatory facilities and so on.
"So effectively this was a very clear case of exploitation".
A GLA spokesman said the adults and children were all being exploited because of the "ridiculously little money they had".
He added: "On current information, all of the families, including the children, are seen by the GLA to be victims and as the investigation continues we expect to find the individual or individuals who are responsible for this disgraceful situation."