You can check bmarcore French shanties page. There's "Matelot puisqu'il fait bon vent" suitable for kids. Also Hugues Aufray's Santiano or Le port de Tacoma as Peregrina mentioned.
My kids at school loved Anne Sylvestre's "Veux-tu monter dans mon bateau?" but they were 1st graders so depending on the age of those you want to teach it, it'll sound childish. It's no traditional shanty, it's a kid song about a boat. You can find the lyrics and an mp3 here but hurry up to do whatever you see fit about it before the blogger being requested to remove the recording since it's under copyright.