What about "A Drop of Nelson's Blood"?

I've taught that in two primary schools to yrs 5/6 and they like it. Teachers like the historical links to Trafalgar and Admiral Lord Nelson. Kids like the sick tale behind the song of Nelson's body being kept in a barrel of rum to take back to England, but they also like the fact that you can get them to think make up new verses (as some of the originals are not necessarily suitable)

Get them thinking about their school dinners for example, or it was very snowy when I was in one school so we did a verse "A day out in the snow wouldn't do us any harm" as the school had been shut.

Quite a few shanties are good for that age group of children because the call-response nature and the simple rhythmic tunes make them so easy to learn. All kids know "What shall we do with the drunken sailor?"