SoccerDrive.com has a handy set of 17 lessons (webpages) for new youth soccer coaches on their Learn How to Coach Soccer page.  The last of these lessons is titled How to Deal with a Poor Referee and provides good guidance.  

Giving constructive feedback to referees can be very helpful, but should not be done during a match..  You may ask if you can chat with a referee after a match, on the pitch, when they are done with their duties.  However, please try to be constructive, specific, and ultimately RESPECTFUL. If they agree to listen to your question/comment and you don't agree with the referee's response, thank them for providing their opinion and if you must, agree to disagree.  The conversation will likely prompt the referee to reflect on their decision while it is fresh in their mind and perhaps prompt them to study the topic or ask a mentor for insight so they can either confirm their decision or perhaps decide to handle a similar situation differently in the future. 
This is much more helpful to the referee than emailing the RRA.

Being a referee is extremely difficult, and the job is made more difficult because most spectators are rooting for only one side.  This inherent bias really does skew our perspective as spectators and coaches (even if referees themselves), whether we think so or not.  So give the refs the benefit of the doubt.  They are a crucial part of our youth soccer program.  Overall, they do a very good job, and they are learning and growing as officials, just as our players are growing and our coaches are growing.   

We cannot have games where coaches and/or spectators question the calls of referees requiring referees to stop matches to deal with the situation. We cannot have incidents, both before the start of a match and/or once a game has ended, when coaches and/or spectators confront referees or other volunteers over decisions made prior to, or during, the game.  AYSO has a “Zero Tolerance Policy” prohibiting such behavior.