Naysayers of the value of early language learning sometimes point out that if students have no incentive to use a language they’ll forget it, and even the most enthusiastic English teacher has probably questioned the validity of “Mummy and Me” classes with pre-verbal students.
Linguists are now showing, however, that early exposure to a language seals it somewhere in the brain, and the building blocks of the language are still there even if the vocabulary has been completely forgotten by the conscious mind.
A study used English speaking participants who had spoken Hindi or Zulu as children but who had forgotten the languages. While they showed no memory of any words or sentence structure, they were able to pick out the phonemes from the forgotten language, phonemes difficult for English speakers to hear.
An example from here in Japan would be students who learn English young being able to clearly distinguish l and r or b and v later in life despite not knowing any English words.
Many of us may have also had the experience of teaching “false beginners”, adult students who feel intimidated by English and seem like they don’t know anything, but turn out to have a decent grasp of English basics once they get reminders and confidence. The English they learned in school turns out to still be there in part, allowing adult students to progress rapidly.
It’s comforting to think that language doesn’t just disappear even without use, and with a little effort we can bring it back. Thus even if it seems like your students aren’t using their English now, maybe it will just sit in their heads until they decide they want to use it in the future.