Solicitor Jill Greenfield said she was instructed by relatives of the "seriously ill" youngster to pursue a negligence claim against Godstone Farm in Surrey.
But she would not disclose her clients’ names or the age of the child involved.
"We need to establish what went wrong and who if anyone is at fault. I would hope that the farm representatives and the Health Protection Agency (HPA) will agree to meet with me as soon as possible in order that I can establish the facts as quickly as possible.
"I have contacted both the farm and the HPA today suggesting a meeting this week and I wait to hear."
The HPA said eight children remained in hospital and 67 cases of E.coli have been linked to Godstone farm.