The following study investigates preschool teacher s experiences of addressing children from different background in order to support Spanish and Norwegian languages in bilingual kindergartens in Norway. The aim of this study is to look at the interactions and strategies preschool teachers applied in kindergarten for enhancing and measuring the progress of language and vocabulary development. The research sub-questions around the topic are as follows: How do preschool teachers mediate bilingual interactions to support language development in bilingual kindergartens? Which strategies do preschool teachers apply in bilingual kindergartens? What resource is used by preschool teachers for assessing language and vocabulary in bilingual kindergartens? This research deals with bilingual kindergartens in Norway which is mostly attending by Spanish, Latin-American and Norwegian children where Norwegian and Spanish language is greatly used as a way of communication between kindergarten staff, parents and children. The study was applied to six participants who work in bilingual kindergartens in the downtown of Oslo. Most of the participants speak both languages in their working place. Through the use of qualitative methods, such as interview and informal observation, I investigate their experiences and challenges relating to language and vocabulary development. The first part of the theoretical framework presents several approaches to the phenomenon of bilingualism including cognitive and socio cultural studies by Vygotsky (1965) and Cummins (2000) that investigate the relation between cognition and cultural factors in the development of bilingualism, later followed by wide spectrum of professionals that investigated vocabulary instruction strategies and languages assessment in kindergartens. The results are divided into three parts: view of bilingualism, strategy use and assessment of language and vocabulary development. First, the results concluded that preschool teachers were highly positive towards bilingualism; they stressed the importance to expose children to natural environment surrounded by people who master both languages. Second, the results concluded a diverse strategies used by preschool teachers and other staff in kindergartens, including the active use of both languages; weekly routines as playing, singing, reading books, indoors and outdoors activities; which correspond to an informal instruction of language. Besides this, the advantages to learn a new language in early years which provides the possibilities to understand culture differences and traditions, disadvantages and challenges they meet in their pedagogy activities. Third, findings suggest that preschool teachers assess languages through observation process rather than making structured or systematic evaluation. All the participants apply strategies that not namely emphasize vocabulary development; the approach used is more focus in language development through social interactions rather than instructional strategies.