In schools from two neighbouring rural towns of Flanders and Wallonia (Brakel en Flobecq) and in the commune of Forest in the Brussels region, school children received an invitation letter to participate in this study. The invitation included an information brochure for the child, an information brochure for the mother as well as a reply card. All voluntary mothers were asked to signed aconsent form. The children wrote their name below an assent document.
Most European countries chose to recruit though primary schools. In Belgium, a total of 13 schools did participate : 5 in the rural area of Brakel/Ellezelles/Frasnes and 8 in the Brussels Region.