I think you're right that it comes down to economics/capitalism. But I doubt it's a conspiracy to boost GDP and tax revenue, as you allude by saying "is good for the economy". I think you're closer to the mark with "economically efficient" -- what seems a more likely explanation to me is comparative advantage:
Sure, grandpa might be a great primary caregiver while mom and dad are at work, but he might also not be. Chances are low he has any training in early childhood education, though he may have raised his own kids -- but he's tautologically not as young as he used to be. But he might have training in law, or medicine, and might plausibly be very valuable as a consultant for the hours that he's instead watching little Ephra.
The licensed daycare in the neighborhood, by contrast, is set up to care for children, and -- depending on grandpa's hourly rate -- might do so at a lower cost. The folks there are (maybe?) trained in early childhood education, and have years of experience handling 1-2 year olds, or 2-3 year olds, or 3-4 year olds, at least compared with grandpa who might only have a year or two of experience with each.
Sure, grandpa might be a great primary caregiver while mom and dad are at work, but he might also not be. Chances are low he has any training in early childhood education, though he may have raised his own kids -- but he's tautologically not as young as he used to be. But he might have training in law, or medicine, and might plausibly be very valuable as a consultant for the hours that he's instead watching little Ephra.
The licensed daycare in the neighborhood, by contrast, is set up to care for children, and -- depending on grandpa's hourly rate -- might do so at a lower cost. The folks there are (maybe?) trained in early childhood education, and have years of experience handling 1-2 year olds, or 2-3 year olds, or 3-4 year olds, at least compared with grandpa who might only have a year or two of experience with each.