My sister told me it's normal. All kids do it. My kid did it more than twice to me.
We were friends on Facebook. Well, it was a break and make 'friendship'. After realising that I know too much of what he did or did not do through his postings, he unknowingly removed me as his friend. And of course, I sensed his 'absence' from FB and confronted him. He was made to add me as his friend again. I believe adding me as his friend earlier was his most regretful thing he had ever done in his life.
Things went on as usual until one fine day when I was again curious about his inactivity on Facebook, I questioned him what had he done to his FB account. After probing, he admitted that he had set some privacy settings to 'block' me. "All my friends do that" was his excuse. So, it's peer pressure again.
Needless to say, he reluctantly reset the settings to normal. Life went on and again today I interrogated if he had changed the setting again. Mumbling some inaudible remarks, he tried to evade the topic. As I was on the computer, he was 'forced' to restore the settings there and then. Guess what! He asked if he could do it other times but I relented.
Without doubt, he must be trying to remove some postings from FB which he didn't want Mom to see. He was lucky that I was on the phone then that I did not stop him from deleting those 'confidential' posts. Still not learning from his lesson, he threatened that he would be quitting Facebook and opened another account on Google Plus.
When being questioned reason for doing it, he rebelled, "I just want to join another social network."
It seems that all kids set privacy settings to their mother who are friends to them for obvious reasons. But, at least my nephews dare not do that to my sisters.