Action for Children Scotland believes misconceptions about who can foster could be preventing more families and individuals coming forward.
In a survey it conducted, more than 2000 respondents believed those likely to be rejected as foster carers include people in rented accommodation, people not in full-time work, men, gay people and over 55s.
With a shortage of 850 foster carers expected this year, the charity says countering the myths is vital to ensure care is available for the hundreds of Scottish children needing it.
A spokeswoman for Action for Children said the charity had been surprised by the lack of understanding of fostering, with some of those surveyed thinking it was little more than voluntary babysitting.
The survey found 99% of people did not know how many Scottish children were currently in care. The figure is about 5000.
More widespread misconceptions included more than half of people in Scotland (52%) believing you could not be approved as a foster carer if you were over 55, nearly one-third (31%) believing you needed to be in full-time work to qualify, people being unaware that foster carers received financial support, and more than a third (34%) still believing gay people could not foster.
Other findings were 8% of Scots surveyed believed a man could not be the main foster carer, and 28% who thought those living in rented accommodation couldn't foster.
Darren Johnson, operational director of Fostering, Adoption and Permanency at Action for Children, said: "With myths preventing people from coming forward, and the public not knowing the true extent of just how many children are currently in care, we are on course for a crisis.
"There's an urgent need to tackle these misconceptions to move children into loving homes so they have the stability they need."
Rising numbers of children coming into care meant the need for carers was inevitably rising, he said.
Children are fostered when they can't live with their own family due to temporary problems, which can range from drug and alcohol abuse to ill health.
But the survey showed many people had little understanding of what fostering actually meant or why young people might be placed in foster care.
Mr Johnson added: "It is estimated it takes four years from someone to think they would like to foster to actually picking up the phone and making their initial enquiry.
"Often the reason behind this delay is because of the misconceptions they have, and their fear of rejection. But this could be prevented by helping people to understand that in the majority of cases they can foster and that they have a lot to offer a young person in care."
In response to the findings Action for Children Scotland has launched an online Fostering Myth Busting Academy on its website. The charity said it could help people understand fostering better and hoped it would empower them to take the first step to opening up their home to a child in need.
The problem does not just affect Scotland. Figures for the UK as a whole reveal that there is a shortage of 9000 foster carers this year with the number of children in care standing at 91,000.
Visit actionforchildren.org.uk/academy or facebook.com/ActionforChildren for more info.