I didn't try to teach them, it is just that both are learning (KGN & PK4) and I keep subtitles on. We've been watching one of the episodes before bedtime since they got off school Friday and when Mommie is working. During the school week, usually no TV/video whatsoever and only a little on the weekends, so this is a bit of a treat. Some scenes in FF are too much for them and quickly get skipped.
BTW, my daughter likes Kaylee a whole lot. My son is partial to Mal.
Also, my daughter was bored by Casablanca, but my son thought it of interest.