But it is also a serious risk period for overeating, say doctors, at a time when many parents are under constant pressure to keep their children entertained.

With six weeks off school over Christmas and January, children often have hours of free access to the television, computer and pantry - a perfect storm for weight gain, according to the expert team at The Children's Hospital at Westmead.

''In the southern hemisphere we have a unique combination of long, lazy summer days, unstructured time and a holiday modality in combination with the major food festivals of Christmas and New Year,'' Gerri Minshall, a senior clinical psychologist at Westmead's Weight Management Program, said.

''When people have a lot of unstructured time, they gravitate towards the television, a bit of cricket, DVDs, computer games and so on.

''You might also be eating some 'sometimes' food while doing that. Putting those two things together can be explosive for weight.''

Ms Minshall spends a lot of time with families providing advice on how to plan for summer holidays and offering strategies to reduce overeating and sedentary behaviour. While she acknowledges that limiting screen time over the holidays can be a challenge, she suggests setting some general rules for children so they do not spend all day on the couch.

''You need to contain it. Say, no TV until after 4 or 5pm, for example,'' she said.

''And you need to set guidelines about not eating in front of the screen.''

Ms Minshall suggests a similar approach to food.

Rather than offering younger children free rein in the kitchen, she recommends putting all their food for the day in a lunch box in the fridge so they know exactly what they can and cannot eat.

Parents also need to plan activities throughout the day to give children more attractive options than sitting in front of the television.

Ms Minshall recommends families take food from home when going on outings to avoid fast food traps at popular children's attractions.

''In general, the food from home is going to be better,'' she said.

''If you go out to the zoo or Darling Harbour, you're at risk of consuming a lot of junk food.''