If you're not picky about your time, I'd expect that there will still be slots available at 9. We sometimes still see slots at 10 or 10:30 even on busy days (and on non-busy days, the shows can be empty - I posted here last month when my daughter was recruited to be kid #12 at the 1-something show so that it didn't get cancelled!) To be clear, for those who know that Jedi Training is a major priority (or who want a certain time slot), it's definitely smart to go early... but you can often get a slot without being there early.
I've also shared this before, but my daughter is 3/3 with doing Jedi Training on a "wait list," and I've heard from others that it's pretty consistently reliable. While I would certainly prepare a kid for the possibility that wait listing won't work out, it seems like in most circumstances, they have plenty of spots (especially for shows later in the day, where more people who signed up in the morning have had plans change). So, as long as you have a kid who can handle that unknown, wait listing can be a viable option if you do find a show is sold out.
As for being within eyesight, not necessarily. You leave the kids at the sign-up area where they get their robes and instructions, and then the parents go to the family viewing area. I suppose you could leave a parent to stay within eyesight of the preparation area (but even then, they might momentarily lose sight of each other while the kids march over). It's also hard to predict where the kid will be located on stage and whether they'll be able to figure out where you are, but they can probably see you if they know where to look.
