Three siblings aged three, six and nine died within 72 hours in Lucknow. Health officials are investigating as post-mortem reports are awaited. A family in Uttar Pradesh's Lucknow has been plunged into grief after three siblings died under mysterious circumstances within just 72 hours, prompting the Health Department to launch an investigation into the cause of their deaths.The children, aged three, six and nine, died one after another between Monday and Thursday.