birdsondabat:
As usual PGStaff has excellent advice. I would only add a couple of ideas that may be slightly off topic but, hopefully, helpful for a coach of a 13 under team.
Make certain that the first runner to reach first base forces the pitcher to throw over to first so all your players can see his move from the stretch to the plate and to first. My experience with that age group is that when they see the move to first, it usually gives them more confidence to take a good lead when they get on base in the same situation. Lefthanded pitchers are especially tricky but many of them give away where they are going [home or first] in advance of their actual release of the baseball by the position of their front foot in relationship to the imaginary straight balk/no balk line between the pitchers knee/foot and the front edge of first base when he raises his front leg off the mound.
Running on the first pitch does have some advantages, at least for the first time you do it [after you have seen some throwovers, of course]. The batter, if he is either taking the pitch or swinging to miss the pitch [only if it is an obvious strike IMHO], will have only one strike after the successful steal in the worst case situation. But I would not make a habit of it because then you will likely see pitchouts on the first pitch to the next batter after your runner arrives at first.
Also, don't give up on stealing third in certain situations. Some pitchers seem to forget the runner on second or, conversely, some middle infielders want to play their position more than holding the runner on. Successfully stealing third one time will usually result in both middle infielders playing close to second base when a runner is on the next time and that creates more gaps in the infield defense between first and second and second and third for ground ball hits through the infield.
IMHO that is the great thing about this game. An adjustment to solve one problem almost always creates an opportunity for the opposing team to exploit that adjustment if they are smart/flexible/skilled enough to do it. I loved coaching third base. Good luck and enjoy the talent you have to work with.
TW344