Two others are missing and dozens have been trapped by flood waters in their homes and cars.
Police say the couple, aged 86 and 85, were found unconscious in their flooded home on Sunday morning, in the seaside village of Politika, about 62 miles north of the capital Athens.
The baby was found in a ground floor flat in the same village. The local mayor reportedly said the baby and its family were not local residents and were on holiday there.
Greece’s deputy minister for civil protection Nikos Hardalias confirmed the deaths and added that there were two more and two people are missing. The names of the dead and missing were not released.
A river has burst through its banks and flooded part of the village of Politika. Other parts of the village are intact. Many residents have climbed to the rooftops of their homes and the fire service has sent a rescue helicopter to the area.
Heavy rain started falling at about midnight on Saturday and firefighters responded to more than 50 fires caused by lightning.
The fire service said it was also called to rescue dozens of people and help many others drain flooded homes. By early afternoon, 47 people had been safely evacuated from their homes and cars, including eight by helicopter, and about 450 homes drained of floodwaters, the fire service said.
Many local roads are impassable, police said. Road connections to the mainland – there are two bridges connecting Evia to Central Greece – have been cut off and only a ferry service is operating at the moment.
