Children as young as four are being treated for obesity because their parents do not understand nutrition, according to teachers.
But now staff are picking up tips on how to make PE lessons and healthy eating more fun as part of The TES's Get Active campaign.
Thousands of teachers visited the Early Years and Primary Teaching Exhibition at Manchester's G-MEX Centre last weekend and joined in practical workshops organised to support the campaign.
Pat Holland, a nursery nurse at Bolton's community college in Lancashire, said: "We have a four-year-old at our nursery who is under a dietician's care to combat obesity. That is terrible.
"We look after the children's packed lunches and see what they are being fed. We have parents who regularly give their child just a Pot Noodle for lunch. It is very worrying.
"We struggle to find activities for the children as most traditional games are too old for the pre-school pupils," she added.
Teachers at the workshops, organised by Steps Professional Development and Brilliant Futures, were encouraged to work together using hula-hoops, gardening canes and skipping ropes to create games that helped to teach children basic movements and aid problem solving.
Samantha McDonald, a supply teacher from Greater Manchester, said childhood obesity was a nationwide problem, not simply a regional one. "Children in the South are at just as much risk as those in the North," she said.
"I have been to schools where all they are offered for snacks are chocolate, crisps and cans of pop.
"Encouraging the children to come up with their own games and activities helps to make them more responsible for their own fitness. I am also hoping to encourage our children to pester their parents for healthier food."
Nikki Brown, organiser of the Steps workshop in the exhibition's Get Active zone, and a former teacher of 13 years, said attitudes about PE had to change.
"When I trained to be a teacher, I spent only four weeks out of a four-year course on PE," she said.
"We are trying to change attitudes by getting teachers to practise 22 basic movements with the children that are used for all physical activities."
Joanne Diamond, of Preston, Lancashire, said she often struggled when taking PE classes. "Being a supply teacher I am told to teach what is already set, but I have found it difficult to come up with healthy activities that keep the children amused," she said.