DD10 joined her school's FLL robotics club (they meet and play with the robot/missions but don't compete) last year, and moved up to the competitive team this year. I got my first look at what the heck it was all about when they competed, then let my DD give me a quick tour of the programming tools, and joined the team as a mentor.
I think it's a great program. Anytime I've looked at a programming manual, my eyes have glazed over. But, give me a real problem to solve, and it suddenly gets interesting. FLL provides exactly that... real, interesting problems that the kids get to solve. There's no better teacher.
In order to hit the ground running, I'd advise you to view some Youtube videos of FLL competition entries, to get an idea of what they're up to. Also, read everything you're supplied when you join, because there are a lot of complicated rules for competitions, and they encourage out-of-the-box thinking by saying, basically, if there's no rule against what you want to do, go for it.
The programming tool is pretty simple... a GUI interface with drag-and-drop blocks that get connected together by "wires." And yet, I've seen enterprise software development kits that looked pretty much the same, so don't let that fool you... these kids may not be doing so through a text editor, but they are definitely programming.
I found that the kids needed some guidance in how to organize their approach to a problem, shown how the robot can be used to take precise measurements, and did not find conditional processing or programming loops to be intuitive at all, so those needed some explanation. Otherwise, they pretty much took to it like ducks to water.
My major job was to watch their programs run, and act as a debugger, because they could often tell what was happening, but they didn't always know why, or if they knew why, they didn't have any ideas on how to approach a solution. So I would ask them what they saw, and then I'd share what I saw it doing, and we'd talk about different ways about how, now that we'd defined the problem, it could be resolved. What I noticed was that, after we'd done this exercise a few times, they started noticing the imperfections on their own, and became more independent of my input for solutions. Practice solving problems leads to problem solving skills... who knew??

If the kids are serious about competing, then:
1) All of the programs need to eventually run on one robot at competition, but we found that having only one or two working robots for the team led to a lot of wasted time by the kids, hampering development.
2) The teams that did best had the most hours of practice, and had the most adult mentors. Our team met one hour a week and had two adults in the room. One of the teams that beat us met for several hours a week, and each kid had a parent with them.
Of course, getting caught up in WINNING! can also mean the adults take over and ruin everything for the kids, so beware. You want this to be child-led. We didn't touch the programming environment or the robot, unless there seemed to be a technical issue outside of what they were doing, or unless we were demonstrating something.