B. Consequences
1) Mental development Just as children's excessive use of computer have negative effects on them [7], children with higher smart phone addiction rate of are likely to have problems with mental development such as emotional instability, depression, Attention Deficit Hyperactivity Disorder(ADHD), anger, and lack of attention [1], [4]. Because smart phones provide sensible and instant stimuli through visual sense and hearing sense, overuse of smart phones is likely to make children who are mentally premature, unstable [13], [26]. Smart phone itself is very playful and immersive [3], so when parents do not let them use it, children have higher chance of being depressed [9]. Furthermore, it causes mental immaturity like aggressiveness and lack of attention [26]. Smart phone addiction, similar to internet and game addiction, also bring results such as children's lack of attention and self-control [19], [21].
2) Physical development Higher smart phone addiction rate predicts problems in physical development such as impairments in visual/hearing senses, obesity, body imbalance same as game addiction of children [14], [22], [25], [26]. When you look at the screen light continually, it is bad for eye health of adults, but children are likely to have more severe impairment in visual sense. Also, when you use smart phone for a long time with earphones, bad effects on hearing sense are expected. When you are addicted to smart phones, you have lower chance of interacting with other people [25], and decrease in physical activities will increase the possibility to be obese [3]. On top of that, operating small device with your hands for a long time might result in body imbalance. Children are incomplete in physical development yet, so overuse of smart phones will cause negative effects on children's physical development in many aspects. IV. CONCLUSION This study examined the antecedents and consequences of children's smart phone addiction. Children are have not reached the age to make rational decisions yet, so they can easily be addicted to smart phones. When they easily use parents' smart phones as their toys, and also parents use them as tools to easily take care of their children, smart phone addiction among children is likely to occur. Antecedents of smart phone addiction among children were divided into parental variables and child variables. When parents' education/income/age are higher, dual-income family, the longer parents themselves use smart phones, permissive parenting style, and positive attitudes towards smart phone, children tend to have higher possibility to be addicted to smart phones. Related to child variables, younger children, boys, children with less siblings, and not attending education institution, predict smart phone addiction. Children with smart phone addiction show problems in mental and physical development. In other words, a child addicted to smart phone has higher possibility of having problems in mental development such as emotional instability, attention deficit, depression, anger, and lack of control. Also, physical problems such as impairments in visual and hearing senses, obesity, body imbalance, and lack of brain development are found. Smart phone addiction among children is likely to be continuous throughout the life time, and because of this, there is big personal and social loss. So, efforts of parents and society to prevent the addiction are needed. First, parents should strive to spend more time with their children. Parents should realize the strong influence of smart phones on their children and it is important not to easily give smart phones to children. It is critical to understand that a convenience of a moment can cause serious results of children's smart phone addiction. Because children have weak control of themselves, they are in need of parents' control. Especially when parents themselves have generous attitudes towards smart phones, dual-income family, and permissive style of parenting, special attention is needed. In addition, efforts of the society are required. Education institutions such as kindergarten and preschool should teach children not to overuse smart phones. Also, phone companies and application producers should develop techniques to limit the approach in order to prevent children from using smart phone too much or addicted to it. Smart phone is surely a good device which made our live rich. However, this tool can be a threat to our children, the future of humanity. Parents and the society should strive to minimize the side effects of this without cease, because children are the most valuable future resources that cannot be replaced with anything else. This research has only proposed research model through literature reviews. In further research, verifying the contents of the proposed model through empirical study is needed.