Indulgent grandparents may be having an adverse impact on their grandchildren's health, say researchers.
The University of Glasgow study, published in PLOS One journal, suggests grandparents are often inclined to treat and overfeed children.
The study also found some were smoking in front of their grandchildren and not giving them sufficient exercise.
Lucy Peake, of the charity Grandparents Plus, said grandparents needed to be "better recognised and supported".
"Grandparents want the best for their grandchildren, and the more they're informed and enabled to play a positive role in their grandchildren's lives the better things will be," said Ms Peake.
The researchers looked at 56 studies with data from 18 countries, including the UK, US, China and Japan.
The report focused on the potential influence of grandparents who were significant - but not primary - caregivers in a child's early years.
The study also found that grandchildren were perceived to be getting too little exercise while under the care of their grandparents.
Physical activity levels appeared to be related to whether grandparents were active themselves, or whether there was appropriate space where children could be active.
Some grandparents actively promoted exercise by taking grandchildren to sporting events or the park.
But where grandparents were sedentary, children were likely to be too.
