She is just eleven but XH has other children aged 12 and 14. They haven't had contact with each other since they were all babies.
I decided to set up an account which was password-protected and very closely monitored so that DD could see photographs and exchange messages. As a nice way-in to keep in touch before we thought about taking it further. And when I say "monitored", I was sitting next to my daughter every time we accessed it.
Obviously I have been more concerned about DD's privacy settings but last night I logged on out of curiosity and saw "sexy schoolgirl" pictures posted by her half-sister (12) and all her friends. Every one of the friends tagged had wide-open profiles. Also, both DD's brother and sister have over 300 "friends"
and their wall posts are visible too.
The childrens' mother has previously assured me that she kept tabs on Facebook and I believed her. Her profile is also available and has interesting posts about the recent riots 
AIBU to have effectively reneged on the idea of FB contact initially?
DH thinks that I have given them a decent chance and found out exactly what sort of parenting (if any) goes on. I am in two minds. They are only children.