This is because they build separate but equally strong language systems in their brains for each of the languages they hear. These separate systems allow children to learn more than one language without becoming confused. In fact, the pathways infants develop in their brains for each of the languages they hear are similar to the single pathway developed by children who are only exposed to English. At 6 months, children begin to notice differences between languages and may begin to prefer the language they hear more. This means that parents must be careful to provide similar amounts of exposure to both languages; otherwise, children may begin to drop vocabulary of the language to which they are less exposed.