Parents are being advised by experts not to give their children food containing certain additives until the results of a new study are published.
Some ready meals contain additives
UK researchers tested the effects of a range of artificial colourings on children's behaviour.
It is understood the results back previous research linking additives to hyperactivity and poor concentration.
The Food Standards Agency (FSA) said it would not issue formal recommendations until the findings were published.
But independent experts said parents should avoid foodstuffs containing the additives.
A team at the University of Southampton tested the additives tartrazine (E102), ponceau 4R (E124), sunset yellow (E110), carmoisine (E122), quinoline yellow (E104) and allura red AC (E129) on both three-year olds and eight-to-nine year olds.
The amounts used in the study were those that an average child might consume in a day.
A source at the University told food industry magazine the Grocer that their results supported findings first made seven years ago that linked the additives to behavioural problems such as temper tantrums, poor concentration, hyperactivity and allergic reactions.
The FSA's Committee of Toxicity on Chemicals looked at the original research, known as the Isle of Wight study, which had concluded removal of such colourings from childrens' diet would produce "significant changes" in behaviour and not just in those children already showing hyperactive behaviour.
But the Committee decided in 2002 the research was inconclusive.
At a recent closed meeting the Committee noted the "public health importance" of the new findings but the results will not be acted until published in a scientific journal.
The FSA said it would be handling the findings in "the proper scientific way" and hoped they would be published in a matter of months.
All the additives tested in the study are approved for use in the EU and are safe but some of the colours are banned in Scandinavian countries and the US.
Pru Leith, chair of the School Food Trust said she hoped the findings would be published quickly but the FSA had to follow scientific protocols before making recommendations.
"We are very keen to promote fresh healthy home cooked food and if you get that sort of food you don't have to worry about additives.
"There is a lot of anecdotal evidence from teachers and parents about children behaving badly when they're given sugary food stuffs so in the end I'm sure we will have the corroborating evidence."
Professor Vyvyan Howard, one of the experts on the FSA's Additives and Behaviour Working Group said it was important the findings were published but that consumers could choose not to buy products containing the additives.
"It is biologically plausible that there could be an effect from these additives. While you are waiting for the results to come out you can choose not to expose your children to these substances.
"These compounds have no nutritional value and I personally do not feed these sorts of foods to my 15-month-old daughter."
Sainsbury's will next month become the first supermarket to ban artificial colours and flavourings in its own-label soft drinks.
Other major supermarkets are also reviewing their policies on additives due to pressure from parents.