The following is some points that you could keep in mind whilst questioning the children. People already have their own assumptions about the credibility of a child's testimony. For instance, Leippe and Romnancyk (1989) found that adults will judge a summary as more reliable if it is believed to come from an adult rather than a child. However, it would be a good idea to shake the confidence of the child, without bullying, as Nigro et al (1989) found that child witnesses who appear confident are judged as more credible than adult witnesses. It may also be a good idea to point out that until recent changes in legislation children under six were considered incompetent to testify and that when children did testify in court, the judge had to formally warn the jury that they were listening to a child. This may help to discredit the children's testimony.
It may be useful to mention to the jury that Piaget (1932) interviewed one hundred children about lying and honesty. From his findings he argued that children younger than six years old cannot identify statements containing a lie and that children do not have an adult understanding of truth and lies until after the age of ten. Therefore, you could try to show the children's limited understanding of what is true and what is a lie when questioning the children. This would make the jury doubt the evidence given by the child. .
Psychological research has suggested that children can be suggestible and leading questions can have a huge effect on young children. For example, Lepore and Sesco (1994) conducted an experiment where four to six year old children played with a man called "Dale". The children were later interviewed about his play session. For half of the children the interviewer remained neutral after the child recalled an action, but for the other half of the children, after the child recalled something the interviewer would interpret the response in an incrimination way, for example "He wasn"t supposed to say that".