Children are frequently manipulated by commercial websites claiming to be child friendly, according to research released this week.

A study released by Consumer Reports WebWatch and the Mediatech Foundation found that it is common for children as young as two and a half to go online, and that the most popular children's sites are "moderately" to "heavily" commercialised.

Online games observed by the researchers varied widely in quality, educational value and developmental match with children's abilities. However, the study found that nearly all sites promoted the idea of consumerism.

The most common technique used a reward-for-work model, awarding 'points', 'coins' or 'dollars' that can be used to 'buy' items such as clothing, makeup, big-screen TVs or other accessories for virtual pets or avatars.

Websites frequently tantalise children, according to the report, presenting enticing options and even threats that online creations will become inaccessible unless a purchase is made.

Some sites show attractive options that invite a click but lead instead to a registration form, and some even sell a child's prior experience (a room built for a virtual pet, for instance) back to them using dubious techniques.

Common statements include: 'If you cancel your membership, your belongings will go into storage and will be automatically retrieved when you re-subscribe.'

"Young children love to go online, and we observed examples of wholesome, good quality, web-delivered content," said Warren Buckleitner, editor of Children's Technology Review, and the study's author.

"But after watching 10 hours of typical online play, we were shocked at the extent of the manipulative behaviour.

"This study shows that neither parents nor publishers really know what is going on when children start up a browser. Ideally, the sites kids encounter should be designed by people with degrees in child development instead of MBAs. "

The researchers advised parents to set up the home computer in a central location so that the child can be monitored.

Parents are also urged to suggest an activity that matches their child's interests or abilities, and pay attention to the directions the activities take.

'Free' offers should be treated with suspicion, according to the report. As in the real world, free lunches are rare and this is a concept children cannot understand. "If it looks too good to be true, it probably is," said Buckleitner.

Beau Brendler, director of Consumer Reports WebWatch, added: "We believe parents need a more complete picture of the sites where their young children are spending an increasing amount of time.

"One test family spent $1,316 in a year on stuffed animals on a single site. Some sites play for profit on a child's emotions to such a degree that we saw begging, tantrums and even tears."