Unless they're in a very cloistered community, kids are exposed to the, uh, "host language" very, very frequently. Our toddler has been in daycare since she was fairly young, and started picking up both English and Spanish words. (Her word for "water" remains "agua", in fact; she only recently switched from "abre" to "open".)

(And if they're in a very cloistered community, their parents are probably more focused on the native language instead of the host language anyway.)