It is definitely important to have someone around to teach proper throwing mechanics, fielding, hitting etc at a young age. I think the biggest thing with Kids 10 and under is making sure they fall in love with the game and just not messing them up and building bad habits. But I guess I was also spoiled in that sense bc of my father's own experience in the sport and having a close friend who's dad coached hs baseball.
I played travel ball from the time I was 13 through the summer after my junior year of hs. Didn't play the last summer after graduating bc I knew wasn't gonna be playing in college and didn't really see the point anymore. The experience really completely depends on the coaches involved, what your expectations are, what level of travel team it is, and importantly the structure of the traveling team's organization.
I absolutely loved baseball prior to joining that team. And I had a blast playing for them and loved the game. There was definitely a point though where you reach when it felt like a job. Especially when as soon as hs ball is over you go directly to travel ball, which makes for a ton games. But even as a teenager I remember not getting to do a lot of things I wanted to in the summers and sometimes hoping it would rain occasionally to get a night off. Tbh though it probably helped keep me from getting into any real trouble bc my schedule was packed. Keep the kids busy and its hard to make too many stupid decisions like I'm sure I would have with a bunch of free time on my hands.
It was still an overall good experience, but a big part of that was the kids on the team, the coaches, and managed expectations.
They can be expensive as well, but its not that hard to find teams that stay relatively local. They'll play league games locally M-Thursday and travel maybe 4-5 hours of drive time for wknd tournaments. Most of the longer travel than that is only for the Showcases, different World Series, and major tournaments, so plenty of teams may only make long trips 1 or 2 times a summer, if at all depending on the success of the team.
I think the best age to start a travel team is somewhere in the 10-13 y/o age range. I definitely felt a little bit behind when I was 13 that first season with the big change in pitching and it took me a while to adjust. I remember being frustrated and angry with my dad at around age 11 when he wouldn't let me play for a travel team that asked me to join them mid-season. Looking back though, I think he just wasn't sure I was completely in love with baseball yet, bc as most 11 year olds I was pretty fickle. He probably didn't want me to end up hating the game. So in hindsight I get his thought process but if you know the kid truly loves the game, then I think 10 or 11 is a fine age to start travel ball.
I can't stress this enough though, but if a kid doesn't fall in love with the sport on his own, it doesn't matter how good they are at it. They're almost always gonna end up resenting playing the game at some point and moving on.
Really though, more important than travel ball is just building good fundamentals. A proper hitting stroke and approach (check out Ted Williams book) or google search about rotational hitting and follow that. Cal Ripken has a bunch of great instructional stuff as well out there for fielding. Pitching...well, that seems to be the area with the biggest amount of debate from the traditional approach to the dick mills school of thought, to the many others out there. I'm not really sure which is best for pitching, but I think if you're looking for an instructor the best thing is making sure they can communicate w/o using cliches and are incorporating DVD/video tape analysis.
I know this was long and rambled a bunch, but if you have any specific questions, I'm happy to answer about what my experience was like playing travel ball.