I learned it as "you owe me a farthing," certainly an easier line for a kid to sing than "you owe me five farthings."

I've taken the unilateral action of ditching the stupid line, "Here comes a hatchet to chop off your head." When I sing this it's usually to little kids, and today's little kids don't need anymore reminders of adult hostility and aggression. They get too much from popular culture already.

I sing "Here comes a candle to light you to bed. And here comes a pillow to rest your sweet head."