As I stated earlier, there is a very useful topic regarding money:
I can't get enough money...I wait a few generations before going for the more expensive things in the house as once you have earned a good amount of money, you can click on the "$" next to their amount of money and see how much they'll be earning in the next while.
Check how much money you'll earn using the "$" sign button next to your money total. Each generation lasts about a week long so it can take a long time to start generating a lot of money! Also, if your family really needs medication make sure you always have enough for at least that.