Officials investigating an outbreak of E. coli O157 which may be linked to a petting farm say two children acquired the illness from the same source.
Both children, one from Ceredigion and one from Kent, visited Cantref Adventure Farm in Brecon, Powys, in the days before they became unwell.
Two other people, who are family members of one child, tested positive.
The farm has stopped direct contact between animals and the public as a precautionary measure.
Samples collected from animals at the farm are being tested.