We have seen plenty of these types of apps come thru the forums. Unfortunately most are from unsources/devs that you may not feel comfortable trusting. If I personally was going to allow an application that type of access into my device/accounts I would prefer its coming from a reputable source like from the Google Play Store, Amazon, Get Jar or Slide Me stores. Giving an application this type of access can be dangerous because if its digging into their FB messages it can also be into their contacts and other personal information which in the wrong hands can be bad.
Again this is just my personal opinion, I'm a father of 5 children that have cell phones. I just worry as any parent about the overall safety of our children especially when giving outside access to their personal information over the internet/phones, etc.