If you’re thinking about bringing up your children bilingually, it’s a good idea to make your own definition of bilingualism clear. Language proficiency can be evaluated in terms of listening, speaking, reading and writing. You could also add a fifth area of speech and language, in which a person is able to use one or both languages for reasoning, to your definition of bilingualism. A person may speak only one language but have listening comprehension in two languages. Another may listen and speak in two languages but reading and writing ability in only one.