The simple, common mistake that almost killed Laura Wallis' newborn twins.

Laura Wallis, a Melbourne mum of four, has issued a serious warning to other parents after being forced to watch her newborn twin daughters fight for their lives in hospital.

The six-week-old twin girls, Harper and Harlow, were infected with RSV, a virus often mistaken for the common cold, which can be deadly for small babies.

Wallis took to Facebook to urge people with a cold not to go near newborn babies.

"Please I urge anyone who has a cold not to go near babies this is the result of someone with a cold coming near my babies," she wrote.

"One twin on oxygen and a feeding tube and another heading the same way so please if you are sick even with a minor cold do not go near babies," she added.

Wallis believes a friend passed on the virus when she came to visit them in their home. The mother-of-four warned friends that premature babies are more at risk of germs, and she says she is furious that her warnings were ignored.

"When the girls were born they were five weeks premmie. I explained to all my family and friends that even minor illnesses could harm them and told them not to come over if they were sick," the Melbourne mum told Mail Online.

"I just can't believe someone decided they would be able to risk it with my babies. Now they could die."

Laura's Facebook post has been shared over 240 times, with many people sharing their own close calls.

"My husband had a serious cold when we had our baby, I had to fight with him, so he wouldn't go near our bub. He couldn't understand, he thought I am mean... At least he ended up wearing a scarf around his mouth and nose when he cuddled him. I think keeping a sterile environment around your baby in the first couple of weeks is very important. I hope your twins get better soon!" one person commented.

"Here I sit in my hospital room, three days after the delivery of my twins who are in NICU ATM. They are five weeks premmie and all I hear are little kids running around coughing everywhere. Please leave your sick kids at home. Visits can wait. Hope your twins get better soon," added someone else.

The smaller twin Harper, was the first show symptoms. On Tuesday she was rushed to hospital after she went blue around the mouth.

She was sent home on Wednesday – but on Thursday both babies were sick. So both Harper, and her much bigger sister Harlow, were admitted to hospital.

Keep Your Filthy Smoker Hands Off My Baby on This Glorious Mess. 

Both babies are being fed by tubes and Harper is on oxygen.

Laura has two other children who are being looked after by friends and family so she stay by her daughters' bedsides until they are better.

The Melbourne mum will be reinforcing the 'no sick house guests' policy when she finally gets to take her girls home.