My mother used to sing a song, "Monday at ten, the king, the queen and all the little princes, came to my house to eat, to eat, to eat a dish of quinces." Does anyone know where this song comes from?

I'm not sure where that song come from exactly, but I go to a French school (in Canada) and we sing it all the time, I think it may be a Quebec folk song 'cause I even heard it in the backround of a French commercial once. "Lundi matin, le roi, la reine et le p'tit prince, sont venus chez moi pour me serrer la pince" It continues, with Mardi matin, Mercredi matin etc. Also in French the song is slightly different, translated it becomes: "Monday morning, the king, the queen and the young prince came to my house to shake my hand..." Here's a website that shows the lyrics in French: https://www.songsforteaching.com/french/lepetitprince.php
I'm pretty sure it's a French folksong and your mother is just singing the English version.

Thanks for that - I clicked on the link - and it is definately the right tune! - so must be related. My Grandfather's brother married a Belgium war bride - so maybe it came to us by way of Aunt Margaurette. She used to teach us French when we were little.