Quincy - I would treat the 4th outfielder as a "short right fielder". You play the SRF on the edge of the grass between your second baseman and first baseman. The beauty of this position is she can make outs to 1B base on ground balls that reach the deep infield, can catch pop-ups or shallow fly balls, and when not fielding a ball, can easily back-up 1B on throws going to that bag.
The other three outfielders (LF, CF, & RF) play their normal depth. However, if there is a runner on 1B who is likely to steal, have the CF play shallow (RF can cheat over to cover right center field) and take the throw coming from the catcher. What I like about CF covering the steal in this situation is that the whole play happens in front of her. She can easily see the runner break for 2B and has both the throw and bag directly in front of her. If you believe in the premise that 70% or more of the balls put in play go to the middle and right side of the infield, that is the place where you have to defend against the hit.
If the league allows you to have a 4th outfielder use it to your advantage. At that age, the goal on defense is to get the maximum number of outs, the most efficient way possible, while limiting the amount of risk for a big inning by the offense. Keep it simple, have fun with a short right fielder, and give your team the best opportunity to make the easy outs.
The other three outfielders (LF, CF, & RF) play their normal depth. However, if there is a runner on 1B who is likely to steal, have the CF play shallow (RF can cheat over to cover right center field) and take the throw coming from the catcher. What I like about CF covering the steal in this situation is that the whole play happens in front of her. She can easily see the runner break for 2B and has both the throw and bag directly in front of her. If you believe in the premise that 70% or more of the balls put in play go to the middle and right side of the infield, that is the place where you have to defend against the hit.
If the league allows you to have a 4th outfielder use it to your advantage. At that age, the goal on defense is to get the maximum number of outs, the most efficient way possible, while limiting the amount of risk for a big inning by the offense. Keep it simple, have fun with a short right fielder, and give your team the best opportunity to make the easy outs.