Sincerely I don't really think the first two reasons you stated is why young girls get pregnant this days,
I might just want to consider the last reason and and speak about it (Lack of good parents)
Good parenting to me should not be holding your female child from going out, locking her in the room and preventing her from friends, as a parent please create a relationship with your daughter so she can be able to tell you everything at every moments, mostly for the mothers, let your daughters see you as a friend that she can tell anything at any given time,be open to your daughters always and give them the acknowledgement that you are always ready to listen to their complains in life and to give a motherly advice..

Teach your daughters everything you know about sex,so she can be cautious and have a clear knowledge about it, also tell her what she needs to know about ovulation period and otherwise,