Yes, wherever you look, there are more gambling ads, especially when you enter social media, you will see only gambling ads. And most of the minor children now use mobile phones, they are so attracted to mobile phones that they can easily see gambling ads. But the most important thing is to be aware, if parents can keep their children away from using mobile phones, most of the children will grow up to be good people, they will not associate with bad people, and now people are mostly going down bad paths only through mobile phones. So if we parents are aware, then we can protect our children, otherwise we will not be able to protect our children.
How can you predict that if parents take mobile phones from children, then will grow as better people that children who use mobiles? From your post, every mobile phone user is a bad person, and as a proof you mention being able to see gambling ads. That does not make sense. Children and parents must adopt to modern world. A person without a mobile, especially a child, will be a lonely person today. For example people dont chat IRL, instead they prefer chatting online. To be on the topic, taking away mobile to improve results in studying also does not work. A child will be more focuses on doing studying as quick as possible with any result or success, only to get back to a mobile.