With teenagers, its that their parents don't always understand what they' re going through, physically and emotionally because their life is almost over and they're jealous that they're childs life has just begun and is probably clingy because they don't want to give up their child. But with children there is child abuse, having ADHD and its not their fault but their parents believe its just an excuse for naughty children. Parent break ups and divorces and step parents. If its at school then bullying could be one. Being the middle child could also be one.