Many people use the internet to find health information
Typing your child's medical problem into Google is unlikely to deliver much in the way of good advice, UK researchers have said.
The Nottingham-based team used the search engine to find UK-based advice on five common issues, including breastfeeding and autism.
Only about 200 of 500 sites offered correct information, Archives of Disease in Childhood reports.
Government-run sites were the only completely reliable source, they found.
It is now estimated that 70% of UK households have access to the internet, and increasingly, parents are turning to search engines for a second opinion - or even a sole one - on medical matters.
Many doctors, however, are concerned that the huge quantity of information and advice is at best unreliable, and in some cases misleading or even dangerous.
One earlier study looking at advice for children with a fever found only three out of 22 sites visited gave information which matched current "best practice" guidelines.
The researchers from Nottingham University Hospitals NHS Trust tested this by typing key words from commonly-asked questions into Google, restricting results to UK-based sites only.
The five chosen were "MMR autism", "HIV breastfeeding", "mastitis breastfeeding", "baby sleeping position" and "green vomit".
They found the quality of advice varied significantly, with half the search results failing to answer the intended question.
In total, 11% of the 500 results gave inaccurate information, and 39% gave the right answer.
The most incorrect replies were given to search results about MMR and autism, and HIV and breastfeeding.
News websites were accurate 55% of the time.
Particularly poor at answering the question were "sponsored links" which appeared prominently, even though the information they contained was not closely related to the search terms.
In the case of the "MMR/autism" search, many of the sponsored links offered single vaccination as an alternative to MMR.
However, the accuracy of governmental websites such as NHS Direct or NHS Choices meant that they should be recommended more widely by doctors, the researchers said.
"Healthcare professionals should continue to strive to be the main source of information for patients but we should be aware that most will continue to use the internet to gather information," they wrote in the journal.
"We suggest that in addition to verbal and written information, patients and parents should be signposted to NHS, governmental or other pre-approved websites."
A spokesman for the Department of Health said NHS Choices was now the most popular health website in the UK, receiving nearly nine million hits a month.
He said: "It offers a range of health information on over 800 treatments and conditions, waiting times and survival rates for elective procedures. Patients using the site are also able to post feedback on hospitals and GP surgeries."