Boats, Streets and Little Sisters

Nathaniel (singing): Row, row, row your boat, gently down the street. Mary, mary, mary, mary, gently down the street.

Me: Nathaniel, it's actually down the stream. And it's merrily, not Mary. Here, let me sing it.
Row, row, row your boat, gently down the stream. Merrily, merrily -

Nathaniel (interrupting): That's not a real word, Mama!