Hunter New England Health has issued a warning to GPs and parents following an increase in the parechovirus infection in young kids locally.
Mild cases can cause respiratory or gastrointestinal illness, while bad strains can cause diarrhoea, fever or even viral meningitis.
Doctor Kat Taylor warns that babies under three months are the most at risk.
"For that reason it's really important that people who are unwell with colds, flu-like illness or gastro, should stay away from small babies.
"If you are caring for a small baby and are unwell we encourage you to wash your hands or use an alcohol-based hand rub before touching or feeding them", Dr Taylor said.