The money you have available at a given time are your funds. If you only get paid once a month, you have to budget carefully so you don't run out of funds between paychecks.
The word funds comes from the Latin word fundus, which means "bottom," "base," or "a piece of property." It's not clear how the noun funds got from property to available cash, but perhaps the connection came because a person could base his financial security on being able to sell his land if he needed ready money. If your kids are low on funds, they will probably hit you up for an advance on their allowances. The request will probably begin something like, "How much do you love me?" Too bad that doesn't work at your bank!