Coach backgrounds/experience

If you do not know the coach and have never seen him/her work with your child: 

1. I would try to observe the coach during both practice and game if I have the chance, to see how he/she interacts with the players, and how they respond. You do not need to be an expert to get a feel for that and if he/she can teach. And got to be able to communicate, be positive (for the most part), but also tough (love) when he/she must.

2. Since I played a little, I would also look what coaching points he/she tries to make, how often and how those points relate to what he/she asks during games. "Run faster" for example does't cut it for me. There is also such thing as over coaching or joy sticking players on the ball or putting a show for the parents ... I can see how someone without knowledge can be fooled so I only recommend this step for parents who are familiar with the sport and feel they understand the game. 

3. Beyond that -on paper- a National type license is important but not necessarily career path "A" since we're talking youth. More importantly, I think years of youth coaching experience is huge, especially if they're parents themselves and understand children. Experienced coaches generally don't need much guidance either. But there is also great value in young, energetic, talented coaches given they have the right attitude, and proper club guidance to develop through mentoring. So for a young coach I would also look deeper on the club director and club culture. 

4. Somewhat unrelated to your question but important if we're talking team/club and not a coach for individual training, is teammates and families. Environment can make or break a deal. They can also be a source for more information about the coach/team/club but can also be a little too subjective.