Dr Eileen Vizard, a consultant child psychiatrist who evaluated Robert Thompson, one of the children convicted, said the atmosphere at their trial was so intimidating that it prevented the children from being able to understand what was happening or to participate in the trial effectively.
She said a charge of manslaughter would have probably been more suitable.
Speaking about the Bulger case, at a conference on violence last week, she said: "It is obvious that very young children couldn't feel in any way at ease. It was extremely intimidating and one really would have to question the true capacity of children in that context to plead their case, to instruct their solicitors and to really understand what the implications of the trial were."
Earlier this month, the European Commission of Human Rights in Strasbourg, said that the procedures used to convict Jon Venables and Robert Thompson were a violation of their rights. Venables and Thompson, aged 10 when they killed two-year-old James Bulger in 1993, were tried in an adult court and then detained at Her Majesty's pleasure.
The commission said that the trial of the two boys at Preston Crown Court placed them in a "highly charged atmosphere". It rejected claims that the court case amounted to "inhuman and degrading treatment", but agreed that they had been prevented from participating effectively, a violation of Article Six of the European Convention on Human Rights.
Dr Vizard said her assessment report on Thompson was not used in the trial because it was deemed to be "unhelpful".
"In practical terms the questions which I was asked in relation to the Bulger case were extremely constrained and didn't allow for any development of the psychiatric evidence. They were very tightly focused questions around the defendants' capacity to understand that the events were seriously wrong," she said.
The commission ruling, which has been referred to the European Court of Human Rights, could force Britain to change the way young children are tried for serious crimes. Normally children below the age of 18 are tried in a youth court. If the trials are for murder, manslaughter or other offences carrying sentences of more than 14 years, the child is tried in Crown Court if older than 10.
Rex Makin, the solicitor who acted for James's father, said that the re-evaluation of the case was "dreadful" for the Bulger family. "It is difficult for them to understand all the nuances of the case and why it is all coming out again," he said.Reuse content