If every spinster drinks the sleeping tea, less cloth will be made, but people will need it just as much. Thus cloth will become more precious, and people will be willing to pay 4/3 of the old price. The kids won't starve.

Instead, someone else goes unclothed.

More generally, if everyone drinks the tea and produces only 3/4 as much, everyone, on average, will be 1/4 poorer. Price movements only affect how the poverty is distributed. (Of course, they also affect what new resources are tapped, what new inventions are made, how hard people will work during their reduced hours, how existing resources are redistributed among their uses, and how effort will be redistributed among the different productive activities, but that is going beyond the purpose of the parable.)