The aim of the present study was to validate thirty-eight picture series of six pictures each developed within the PANCAKE (Pilot study for the Assessment of Nutrient intake and food Consumption Among Kids in Europe) project for portion size estimation of foods consumed by infants, toddlers and children for future pan-European and national dietary surveys. Identical validation sessions were conducted in three European countries. In each country, forty-five foods were evaluated; thirty-eight foods were the same as the depicted foods, and seven foods were different, but meant to be quantified by the use of one of the thirty-eight picture series. Each single picture within a picture series was evaluated six times by means of predefined portions. Therefore, thirty-six pre-weighed portions of each food were evaluated by convenience samples of parents having children aged from 3 months to 10 years. The percentages of participants choosing the correct picture, the picture adjacent to the correct picture or a distant picture were calculated, and the performance of individual pictures within the series was assessed. For twenty foods, the picture series performed acceptably (mean difference between the estimated portion number and the served portion number less than 0.4 (SD < 1.1)). In addition, twelve foods were rated acceptable after adjustment for density differences. Some other series became acceptable after analyses at the country level. In conclusion, all picture series were acceptable for inclusion in the PANCAKE picture book. However, the picture series of baby food, salads and cakes either can only be used for foods that are very similar to those depicted or need to be substituted by another quantification tool.