OP, YABU for expecting a free housekeeper when the kids are small. She's your mother, not a servant.
But DM is BU for expecting free round the clock care for her old age, which will probably last well over 20 years. You're her daughter, not a team of four carers.
Anyone who wants to swap childcare for eldercare is pulling a fast one on you.
Bear in mind that old age lasts a hell of a lot longer than childhood does now, and the dependent stage is a lot more technically difficult, expensive and unrewarding.
The world is set up to take dependent children off you for hours a day - schools, afterschool clubs, playgrounds, etc. All this is free, or nearly.
After a few years, children stop being so dependent.
During this time, women get maternity allowances then go back to work.
The dependent old are dependent 24/7. There is precious little in the way of resources or breaks for the carer, and what there is will always be expensive.
After a few years, the old get more dependent.
During this time, women get 0 allowances and cannot return to work.