f/5.6 is difficult to get a good seperation from the background so would suggest to get a little creative. Move your position if possible (though we all know that can't always be done). Also, try to up the ISO to get a higher shutter, ISO 400 or so and you'd be shooting 1/1600 or 1/2000 - something better to freeze the action even better. Or as suggested ditch the 2x for everything except maybe middle infielder shots and open up to f/2.8 as it gives a far better seperation. The below is just suggestions and I know that you don't always have the freedom to move where you want so take with a grain of salt on that aspect, also with smaller kids it's sometimes impossible to get lower like suggested unless you're laying on your belly on the field since they are so much shorter usually.
#1 - tighter crop, move to the side to get rid of the SS and LF'er in his direct background. The light looks a bit strange from the shadow there but what can you do with that except move position where it's less noticable.
#2 - good timing, higher shutter and it freezes the dirt and ball a bit better.
#3 - straighten it by using the poles in the background as reference - you can see the pic is tilted by looking at them. If that fence ends on the left where it looks like it ends (gets lower) then if possible move over and get out in front of him and lower to make the trees the dominate background.
#4 - timing is very good getting it off his fingers like that, not always an easy shot to get. Only suggestion is again getting lower to make the trees the dominate background.
#5/6 - similar shots, would again get lower and move to get the shortstop a bit over and out of the immediate line of view.
#7 - ahh, if only the ball was farther back so he was facing you more, but what can ya do. Tigther crop like in #8 maybe or even just from the right end of the dugout to just beyond his helmet.
#1 in second post - walk around the back stop and slap all parents sitting there until they move. As a coach high school coach I don't allow parents to sit back behind there, they can come take some pics from there but not set up camp.
...as for the suggestion to get on the pitchers throwing side, true but can get boring. Always good to get a few "stock" images of the delivery but when a kid/player has a good follow through like in #3 with the high leg kick it makes for good images that are a bit different than the normal pitching ones.