Not a moment too soon, this motley crew (with Mowgli's four-footed friends racing to the rescue) convenes at the Bandars' fortress ruins. There, to absolutely no narrative effect, they encounter King Murphy, a raving old soldier played by Roddy McDowall, and some cobras, which lack the poisonous pizazz that used to make them such welcome members of the pit bands in the days when story makers like the Korda brothers and George Stevens roamed the Raj in story like ''Drums'' and ''Gunga Din.'' Old-fashioned adventure has fallen on hard times. The Second Jungle Book is rated PG (Parental guidance suggested). It is built around efforts to kidnap and murder a child.