Can natural food color affect the behaviour of small children?

It can't take away from colours. 
Colour is an important property of foods that adds to our enjoyment of eating. Colours enhance the appearance of certain foods to meet consumer expectations. Colour additives belong to one of two groups: pigments derived from natural sources such as vegetables, minerals or animals and those not found in nature and must be man-made.
Most food colours must meet certain legal criteria for specifications and purity. Also, in view of the fact that all additives are subject to ongoing safety review, each substance is tested to ensure that it is safe at its intended levels of use before it may be added to foods.
Although during the last years some theories have claimed that food colours could affect behaviour, at present there is no evidence that food additives cause hyperactivity or learning disabilities in children. However, one colour, listed as tartrazine, may prompt itching or hives in a small number of people. Whenever tartrazine is added to foods, it is listed on the product label. This allows the small portion of people who may be sensitive to the colour to avoid it. This colour should be eliminated from the diet of children.