There are two methods through which children learn multiple languages. Sequential bilingualism occurs when a child is first taught one language, and upon mastering it, begins to learn another. In contrast, simultaneous bilingualism occurs when the child learns both languages at the same time. Simultaneous bilingualism occurs within the first year of life, whereas the sequential acquisition of a second language can occur at any age.
A child who is a sequential language learner would learn one language (e.g., Spanish) until the age of 3 or older before being exposed to a second language (e.g., English). Many times, sequential learners are exposed to a second language once beginning school.
A child who is a simultaneous language learner would be spoken to in both languages (e.g., Spanish and English) with even frequency so that he or she is receiving the same amount of exposure in each language. As early as 4 months old, a child is capable of discriminating between their two languages.