The tribute was paid to five-year-old Mason Jones, a pupil of Deri primary school in Bargoed, Caerphilly, who died. Mason's mother, Sharon Mills, was present at the inquiry in Cardiff along with parents of other children who fell ill with the E.Coli poisoning last September.
She said: "Losing Mason was devastating and I would not want any other family to go through this. Lessons must be learnt."
A total of 157 people contracted the 0157 strain of E.coli across four local authority areas. Professor Hugh Pennington, heading the inquiry, said he would "leave no stone unturned" investigating the causes of the outbreak. However, he also said it could not risk prejudicing criminal proceedings.
"One inevitable consequence of this is that the inquiry cannot simply move forward to a detailed public examination of all the issues," he admitted.
Mark Harvey, a solicitor speaking on behalf of the family support group, said: "The families welcome the start of the official inquiry. They desperately need to know how it happened."