The paper presents the first findings of the children's subjective well-being survey in Poland, which was conducted among representative sample of over 3000 pupils aged 8, 10 and 12 years from Wielkopolska region in spring 2014. The study is a part of International Survey of Children's Well-being (ISCWeB) - Children's Worlds, developed by the International Society for Child Indicators (ISCI). The main purpose of the ISCWeB project is to gain a broad knowledge of children's lives, their relationships with family members and friends, daily activities, time use and, in particular, their own perceptions and evaluations of their well-being. A particular attention in this paper is paid to the children's subjective well-being including overall satisfaction with life, measured with use of different psychometric scales, eg. the single item scale on Overall Life Satisfaction (OLS) or the five-item Students Life Satisfaction Scale (SLSS5). Along with overall well-being of the children, it is very important to study various domains of their well-being. In the paper we took into consideration children's evaluation of their five important life domains: family, school, friends, living environment and self.