This paper is examining the effect of bilingualism on children’s cognitivedevelopment, and in particular, executive function. Different studies report that bilinguals are more effective in focusing attention, inhibition, working memory and in ignoring incongruent information. Some studies indicate that individuals who learn a second language are more creative and better at solving complex problems than monolingual peers. According to these theories, we assume that Hungarian-Serbian bilingual children will also show these increased executive functions. The 50 child participants were divided into two groups, Hungarian monolinguals, and Hungarian-Serbian early bilinguals, in accordance with the Language Knowledge survey. The tests for examining different aspects of executive functions are accessible from the Psychology Experiment Building Language and Inquisit 4 Lab system. On the basis of the results, it can be concluded that bilingual children were more effective in terms of EF. Second language learning in the sensitive period for language will secure more effective solutions and execution in more cognitive aspects. Besides being able to create more social relationships due to their language knowledge, bilingual people will also have advantages in many cognitive processes. Keywords: early bilingualism; executive functions; inhibition; monitoring; cognitive flexibility; cognitive developmentIntroductionThere was a view, that childhood bilingualism has a negative effect on the development of the mind because the two languages will disturb each other (Barac & Bialystok, 2011), and children would display mental confusion or mental retardation, therefore, scientists have been examining how the simultaneous use of two languages (parents have different mother language, using a new language in a new country where the person recently moved, or there are a countries where the official language and the language of minorities are different) affect the development of thinking and language of children.