Parents' assessment of children's development in the first and the second language is an essential part of their family language policy (FLP) and an important component of parent-child communication. This paper presents a pilot study focused on Russian-speaking immigrant parents' assessment of their children's language knowledge in Russian as a first language and Hebrew as the second language in the context of their FLP. The research questions were as follows: How is parents' assessment of their children's bilingual language development linked to their choice of bilingual versus monolingual preschool education? To what degree are parents' reports of their children's language knowledge similar or different to their children's actual language knowledge? Which domains of language knowledge do parents relate to or ignore when assessing their children's language development? The sample consisted of 27 children (14 from bilingual and 13 from monolingual kindergartens), and their parents. Two sets of measurements were used, one to obtain parents' reports on child's knowledge of Russian and Hebrew and the other to assess children. The finding points out parents' insensitiveness to the length of the children's utterances and their tendency to rationalise FLP by overestimating their children's general language knowledge. (Contains 2 figures and 3 tables.)