Two-fifths of parents think that trying to address weight problems could lead to their child developing an eating disorder such as anorexia or bulimia.
The figure rose to 65% of parents who identified their child as being overweight or obese, according to the research conducted on behalf of Netmums and non-profit organisation Mend – Mind, Exercise, Nutrition - Do it.
The study of 1000 parents with children aged five to 16 found many believed that such conversations could lead to low self esteem.
Two-thirds of parents said they would like more support in talking to their child about weight.
Mend clinical director and co-founder Dr Paul Chadwick said: "The majority of parents of overweight and obese children are taking the courageous step of talking with their child about weight-related issues, despite concerns that by doing so they may also be doing harm.
"Our survey shows that they clearly want and need more help in this area."