This chapter discusses four ways in which researchers have documented differences between bilinguals and monolinguals: delay in language development, acceleration in language development, cross-linguistic influence, and cognitive differences. The detectable differences can shed some light onto how language and cognitive development unfold in all children. Bilingual children may have some differences from monolinguals in cognitive development in terms of communicative competence, theory of mind, strategy use, and selective attention. The bilinguals used more manual gestures while speaking than either English or French monolingual children. The results of the study with younger children suggest that bilingual children may be sensitive to their interlocutor’s linguistic knowledge. Bilingual children have extensive experience of choosing languages for the pragmatic context, such as a particular person or a topic. Bilingual children sometimes use constructions in one language that seem to be based on a structure from the other language.