An eight-year-old Melbourne girl who died of the flu had been sick for a few days with what her family thought was a bad cold.
But on Friday she went into cardiac arrest and six paramedics could not revive her.
Christian Brealey said his "beautiful princess" Rosie died just hours after she took a turn for the worse.
"She had been sick for a few days and we thought she had a bad cold. Never in my worst dreams did I ever think it would end up like this," Mr Brealey said in a statement posted online.
"I'm a walking zombie at the moment... don't know how we are going to deal with this."
The family is active in the Australian Jeep-driving community, and members of the AusJeepOffRoad forums are raising money to support them.
A GoFundMe page has so far raised more than $2800 to help the family.
In a statement released to The Herald Sun, Mr Brealey urged people to immunise their children against the flu.
"We are devastated by the loss of our beautiful, loving little angel," Mr Brealey said.
"We urge everyone to get their kids immunised against the flu and ask only that our privacy is respected and our family given time and space to grieve."
Her death follows the flu death of young dad Ben Ihlow on Father's Day.
"What it does show us is that we have a horror flu season on our hands," Health Minister Jill Hennessy told media on Monday.
There have been more than 13,000 flu cases in Victoria over the past few months, including 95 deaths at aged care facilities.
Eight elderly residents died at St John's Retirement Village at Wangaratta in August and early September.