Grandparents are often extremely fond of their grandchildren and their affection may lead to childhood obesity.
Grandparents tend to indulge, overfeed and protect grandchildren in their care from physical chores, thus increasing their risk of obesity, found the study.
The motive for the action of grandparents is affection and stems from their personal experiences, misunderstanding and poor recognition of the adverse health effects of childhood obesity.
Children cared for by grandparents also consume unhealthy snacks and drinks more frequently.
"Our study reveals that grandparents contribute to childhood obesity through inappropriate perception, with many sharing the belief that fat children are healthy and obesity-related diseases only happen in adults," said co-author Bai Li, research fellow at the University of Birmingham.
Grandparents will often assess weight status by comparing their grandchildren with their peers, rather than seeking professional opinion.
"The inappropriate behavior of grandparents, including overfeeding and indulging through excusing the children from household chores, is another contributing factor, and differs greatly from that of parents, carers and school teachers," said Li in International Journal of Behavioral Nutrition and Physical Activity.
"This study highlights the need to include grandparents in future interventions to promote healthy behaviors among children," said co-author Peymane Adab, Professor of public health, University of Birmingham.
"It is imperative that we now work with families, stakeholders and Chinese governmental bodies to tackle this pandemic," said Adab.