Cui Ying, a mother in Beijing, is also screening the apps downloaded on her tablet, and rationing time spent on the device.

Her secret is using educational apps that are updated often, but not too frequently.

Currently, her daughter has been playing with a games app that updates once a day after the 20-minute session is finished.

"When one session is over, she has to wait for a day before the next one comes," Cui says."Such apps are interesting and informative, but will not be addictive."

Cui is happy that her daughter is contented with her daily quota on the iPad, and her vision stays sharp.

"You can't stop kids playing iPad entirely. A better way is to make them realize the iPad is just another average toy," Cui says. "I don't see anything bad if it is used correctly."

Experts agree that parents need to supervise their children's time spent on watching television, the computer and now, mobile devices such as the tablet or cell phone. This is important for healthy physical and psychological development, they say.

Children have smaller eyeballs and have to exert their eye muscles to concentrate on small screens.

Prolonged sessions with iPad screens with animated texts, images and backgrounds will increase the likelihood of myopia and other eye problems.

The sedentary postures also aggravate the situation, according to Zhou Zhe, an ophthalmologist at Beijing Tongren Hospital.

Children in their pre-teens and teens are in the most important phase for bone building. If they stay in a fixed position for too long, it will affect normal, healthy bone growth.

"Many parents know the tablets or computers may harm their children's eyes, but they are less aware of the harm to bone development and structure," says Liu Zhongjun, director at the Orthopedics Department of Peking University No 3 Hospital.

"Once the bones develop abnormal growth, it is very hard to reverse."

The most vulnerable bone structures are the cervical, thoracic, and lumber vertebra, and there are more and more children with unnaturally curved necks, due to an over-indulgence in digital devices, and bad sitting postures, Liu adds.

In addition, children left alone on the computers may be risking psychological damage.

"Children under middle-school-age are fast learners of how to communicate and play out their social roles," says Pang Yu, a psychologist and deputy director with Beijing Huilongguan Hospital, a leading mental institution in Beijing.

"If they get too immersed in the cyber world and miss real opportunities of communicating with others, they may delay language and intelligence development, or have difficulty dealing with inter-personal relationships later in life."

Studies have shown that children who overdose on television tend to receive information passively and lack communication skills. The same problem is surfacing with children who are left alone to use computers, tablets and cellphones, Pang says.

Parents must be there for their children.

There are no substitutes.

"When there are others around to communicate with, children can make use of the iPads to create conversation, rather than to play alone and in silence," Pang says.

"It is very important to keep your children company."

Contact the writers at liuzhihua@chinadaily.com.cn and sunye@chinadaily.com.cn.