What are the most worrisome issues for parents with 7 to 12 years old children around screen addictions like iPad & iPhones?

I would think it is the easy availability of information that could be gathered off the internet. It is difficult to teach children how to be discerning about the information they read off the net. Another issue would be the over reliance on the gadgets and neglecting "real" human interactions. Though I think going to school would greatly help since a large part of their days would be spent in school around their teachers and friends. That being said, it is still important to ensure that a child is not spending too much time using the gadgets. Just my personal take.

Promo terbesar expert care sudah dimulai, diskon hingga Rp.100.000 sedang berlangsung di shopee, ada juga voucher diskon 100% alias gratis bagi bunda yang beruntung. Buruan cek di https://shope.ee/9UfEMMqqTg (id-15899)

I chanced upon this post which addressed your question: http://nypost.com/2016/08/27/its-digital-heroin-how-screens-turn-kids-into-psychotic-junkies/ The addiction itself is the most worrying concern. Have a read.