What is a disadvantage of Maria's staying home with her children until the youngest is of school age?

Maria may not be able to retire at an earlier age. This is because she sacrifices here years of employment by not being economically productive. Her husband has to meet the family expenses single-handedly through his income. Lot of money is spent on child care so they will not be able to save money for their retirement.

To take an early retirement one should have saved quite an amount of money. This will increase the working years for her and her husband.