The Yo Yo Water Ball, this summer's fad toy, has consumer-safety advocates alarmed. They warn that the rubber toy poses a strangling hazard for kids. Some parents say their children have managed to swallow the liquid inside, which in some cases has proved to be flammable and toxic. Consumer-protection officials in New York and Massachusetts are urging the product's removal from stores. Peter Tiger, CFO of Imperial Toy Corp., one of several wholesalers marketing the toy, says his company has sold almost 10 million of the yo-yos and insists they are safe.