The stream of Cuban refugees setting out for U.S. shores all but stopped amid weekend storms, and has since remained a tiny fraction of last week's level of 3,000-plus per day. By late afternoon, U.S. Coast Guard vessels had picked up only 110 or so Cubans in the Florida Straits. But, after hearing reports that dozens more people were milling on Cuban beaches ready to go, Administration officials stopped short of declaring a trend. In Cuba yesterday, Fidel Castro said he had ordered police to prevent people from endangering children by carrying them on rafts and other makeshift vessels. The slight softening of policy may be a preview of U.S.-Cuban talks on the emigration crisis, set to begin in New York Thursday.