In addition to the obvious benefits of learning a second language as a child (such as being able to interact successfully with people from other cultures in school, travel, social, and future employment situations), research also shows that early bilingualism is good for the brain.
In their article, “Bilingualism in the Early Years: What the Science Says,” Krista Byers-Heinlein and Casey Lew-Williams point to studies that show that bilingual children are more adept than their monolingual peers at switching back and forth between tasks, as well as being better able to apply previously-learned responses to new situations. The theory behind these increased aptitudes is that bilingual kids regularly switch between languages and even cultures, and as a result, they must pay attention to the sounds, vocal cues, and facial expressions that other speakers make.
In addition to the cognitive advantages, early bilingualism is correlated to improved social functioning. Byers-Heinlein and Lew-Williams found that “bilingual preschoolers seem to have somewhat better skills than monolinguals in understanding others’ perspectives, thoughts, desires, and intentions” (Bialystok & Senman, 2004; Goetz, 2003; Kovács, 2009), and young bilingual children have also shown an increased sensitivity to vocal tone (Yow & Markman, 2011).
Again, these social advantages are tied to the child having to work between two languages. By necessity, the child is attuned to subtle differences and cues that indicate their different languages and worlds. Learning a second language at an early age, much like learning music, is an effective way to teach the brain the creativity and flexibility to adapt to new situations with greater ease.