Grandchildren? That is to say children of children of Johann Sebastian Bach? No, those lived until the year 1800. Your question probably is, whether there are some great-great ... -grandchildren of Johann Sebastian Bach still living.
Great-great-great-great- great-great-great-grandchildren of Johann Sebastian Bach actually are still living today. There are some seven or eight persons. They however all don't carry the name of Bach. Actually none of them, as the male descendents of Johann Sebastian Bach have died out for a while. At least this is fact until today. However, Johann Sebastian Bach had ever been good for a surprise.
99 Music Calendars, Composers Calendars and Bach Calendars