Jesus Christ. I work in educating parents and children in schools about social media and I'm sorry but your attitude is one that makes me want to bang my head repeatedly on the table.
NO child under 13 should have any social media at all, even if they do feel left out.
Facebook has a recommended age restriction of 13+.
It is there for a reason, as are many of the other age restrictions for a lot of applications.
Six is way too young for any kind of social media, whether or not you feel your daughter maybe left out.
The app Musical.ly is an excellent resource for paedophiles the world around with its gyrating pre-teens desperate for likes and "insta-fame". I've recently been to a conference where the head of the Interpol department for trafficked and abused children was almost punching walls due to the lack of parental supervsion for children online at stupidly young ages.
Your experience on Facebook is no way comparative to what your six year old will experience. Links to all kinds of inappropriate content are easily accessible, a six year old has no concept of what images are appropriate to post online, who she should choose as friends etc.
There is such a thing as a digital footprint that follows you around online. This is a collation of all your online activity. As a parent it is your responsibility to sensibly manage this for your child till they are of an age to understand the consequences of what they post.
Online history is increasingly used for jobs, universities etc to review and determine what kind of person you are. I can't imagine having such a detailed record of all my life availble online for all to view from age 6, and having to clean it all up later.
Social media is proving increasingly damaging to the mental health of the young, with the constant need for validation- concerns about numbers of likes, what they look like in comparison to other photo shopped images etc all proving hugely detrimental especially for females. Anything more than 2 hours a day on social media will seriously mess with your head.
Even a private account at 6 on Facebook is mental.
And if you are going to do this anyway, for Gods sake put something like Qustodio on her devices so you can track what she is doing, and make all accounts private with location services switched off.