Community vigil for siblings who died in shed fire

Three-year-old Saige McGregor and 18-month-old Ashlynn McGregor died at the scene.

Their six-year-old sister and four-year-old brother Isaac McGregor were flown to the Royal Children's Hospital in a critical condition.

Victoria Police confirmed Isaac died in hospital on Wednesday.

People have been invited to pay their respects and show support for the family at a vigil at Rosewall Reserve in Corio at 8pm on Saturday.

"The family needs all the support they can have," organiser Torii Janine Sanderson told AAP.

"As a community we should all stand together and do what we can to help."

It is unclear whether the family will attend or plan to speak at the event.

Organisers say mourners are welcome to bring flowers, battery operated candles, teddy bears and balloons in remembrance of the children.