The main goal of this study is to examine the differences between school-aged children with different chronotypes who are only children or have a sibling in the household, regarding their sleeping habits and performance in intelligence tasks. The main measures used were Chronotype Questionnaire for Children and Raven's Coloured Progressive Matrices. This study analysed 46 Portuguese children (Mean=8.67; SD=1.034, range 7-11 years of age) without sleep or educational/psychological disturbances, attending the first grade. The differences regarding chronotype and whether they were only children or not were examined. Then the performance of the sample in the Raven's Progressive Matrices tests was evaluated. The Mann-Whitney U test showed that 'only' children had higher fluid intelligence scores only in the afternoon. The chronotype did not differentiate this population and it is concluded that the type of household is the main moderator: Not being an only child was, in general, the best predictor in the test. Results suggest that different sleeping times (e.g., bedtime and wake-up time) and different chronotypes did not have different effects. However, having siblings proved to be an advantage regarding the child's performance. Re-education of sleeping practices, especially examining the influence of co-sleeping in families, is essential for the intellectual development of children.