With that many kids the older ones are probably helping raise the younger. My wife's cousin has 5 kids (in relatively short intervals, I think there's less than 10 years between the oldest and youngest) & the 2 oldest ones help out a lot.
So it turns into more of a management role, and less like hard labor. Still not really retirement.
Yeah I dont think you'll be lazying about but also that the difficulty is much less than a linear 12x the difficulty of raising one child.