It could be peer pressure. Other possible causes may be loneliness or the feeling that other Christian youths are doing better spiritually.
وَيُعْطِي ٱلْمُلْحَقُ أَيْضًا ٱقْتِرَاحَاتٍ لِلْوَالِدِينَ كَيْ يُقَوُّوا إِيمَانَ أَوْلَادِهِمْ .‏