To Accept or Not to Accept, That is the Question

So recently two of my second grade students sent me friend requests on facebook. I explained to them that I did not think it was appropriate for me to be friends with them on facebook.  I can't believe that two little girls are on facebook!! Am I crazy or is it not a good idea for 7-year-olds to be on social networking sites? Why would any parent allow their child to be on facebook?  They both told me that their moms knew and thought is was OK for them to have  FB page.  I just think of all the things that can be accessed on the internet not to mention the predetors that on here looking for easy prey.  Am I making too much out f this or not??