In this day and age, adults do not tend to go missing unless they want to go missing. With the use of mobile phones, social networking etc it's easy for a person to get themselves found if they need to do so. But with children they are easy to manipulate, do not often have phones and are small and easily bullied. It's a big world with small spaces and people can easily get put there. I don't really know what I'm saying. Basically. When it happens, usually a lot of planning has to happen. And blahh I dunno. Ignore me. lol
I my country, over the past few years kidnapping has become somewhat of a business for criminals. It is almost scary if you happen to be wealthy. Never mind how hard you worked to achieve your wealth. Another popular reason these days is human trafficking. Children have also gone missing and have never been found.
A lot of ways, they could be killed, they could be kidnapped, they could just go away on their own. Some people sometimes just go somewhere else, get new cells, and get new everything to start new. It all depends on how they go missing, there are a lot of situations.
Runaways, kidnapping, m*rders, getting lost in the woods. Or sometimes its purposely done.
M*rder, they might want to start a new life, accidents.