If you are going to use a smart phone to your son, you should take care that they do not use it and then lose effect with sue and other stories in nong everyday.
If you give your son a smartphone, you should take care that he is not to use it, then the negative effect on the course page book and other matters on a daily basis.
If you want your son to use smartphones, you should take care that they will not use it and be wasted with learning time, books and others in daily life.