Having been a commissioner of a recreational youth soccer league with (at the time) over 1200 kids participating, I can tell you: just show the slightest flicker of interest and you’ll be invited (over and over again, if necessary) to various (mostly informal, to start) clinics in “what to watch for” and “what are the rules, exactly”.
We used to start parents, and even older siblings (even better, usually) as volunteer linesmen on the pitch (soccer field) for the kindergartners who are mostly just running around almost at random, trying to stay upright and avoid knocking into each other. There aren’t many “penalty kicks” and the like at this age. The idea is definitely for the kids to have fun and avoid injury.
But the ball always goes out of bounds, and as a linesman you’d learn how to be in position to spot that (and exactly when it happens that the ball completely clears the bound line, unlike in American football, for example, when the ball touching the line is “out of bounds”), make the best (and quickest) determination you can about who touched the ball last and awarding the throw-in to the right team. Very, very simple, and very, very uncontroversial. Parents of kids at this age level know that it’s not about “the competition” as much as it is about the enjoyment and learning of the game. Generally that feeling extends to the officials. (You’d find that many parents know the rules better than you do, when you start.)
And so it goes. As your skill in making “out of bounds” calls grows (pretty quickly) at this low level, then you’d be easily instructed in making more advanced calls such as on-field penalties, offsides and the like. Before long you’d be officiating at games with more skilled players and faster action (and more parents knowing more about the rules, too!).
Most games at the rec level were officiated in our league by (paid) part-time volunteers who were often just a few years older and more experienced than the players.
I’m sure that most rec softball and baseball leagues operate under similar rules. Liability insurance issues may force some leagues to operate with more formality, but I’m sure they are just as anxious as we always were to find and develop new officials.
Congratulations on your interest. Have a ball!