Child's username - where/how is it used?

[JohnnyRow]

Setting up a child account, I need to enter a unique username that doesn't hint at the child's name.  Trying to figure out what to use, where does this ever show up? Is it ever used on message on tracker or anywhere child will see it?  For the adult account, I guess this is the name with user posts, but children cannot post.  Does it show up on the child's app view? Will the child ever even see this?  If I later realize I made a poor choice here, can I later change it or is this permanent?

And it also asks for child's first name, but then later on asks what name want to use as a greeting?  So if the first name is not used for the greeting, what is it for?

[DramaQueenDiva]

Hazarding a guess here, but I'm thinking that since your child can appear on your Friend's List, they want to protect the identity of the child. 

[Rich_Laue]

This probably has more to do with the federal COPPA Regulations of which Fitbit has to conform with.