1st Lax practice- could use some tips

My son had his first lacrosse practice this morning. He's 7, and the ages were between 6 and 9. This is the first time I've done lacrosse shots since last spring. I'm just using a Canon Rebel Xsi, with a 50-200 zoom lens. I was shooting on action mode, and I totally forgot to check my shutter speed. (I think it was 4. something.....but I forget)

I feel like I could really improve on these, but would like some advice. First of all, where our practice field is, I don't care for the backgrounds. I TRY to make sure there is nothing ugly behind them, but it can be hard. I also feel the color and lighting could be better.

So, can somebody please give me some advice. Also, I would like to know:

A.- if I want to get a better camera body, what would you recommend I get next?

B- What settings do you recommend for this type of sports photography?

C would an external flash help?? I want to get one, but haven't yet.

Thanks so much for ANY help or advice. This was just a practice run, before I start doing games again. (And, I'm just a beginner, not a professional. I do the team pics, and parents buy them. They LOVE them, and had a lot of compliments. But, I don't have my own official business, and know I have a lot of improving to do).

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I like them because they tell a story. They show fun and excitement. You can try bumping up the saturation a tad bit to bring out some of the color and maybe drop the brightness a small bit.

Thanks! So, does this look better, or is it a bit TOO much??

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You can turn your f/stop down it's lowest setting. This will blur the background a bit. I always try to shoot pictures at a 45 degree angle. So like in picture 1 and 2. The players look flat because you shot them straight on. Picture #3 is what looks good. I always like to get as low as possible, especially with kids. Your shutter speed could be slightly higher. But you pretty much stopped the ball in motion. You can shoot loose like you did, but when you are editing your photos crop tighter, and fill the frame. This will also eliminate the background you don't like.

My son also plays youth lacrosse. I have found that if I sit at the midfield line, I need a 300mm focal length to shoot from goal to goal (70-200 with an extender). At 200 mm, I usually need to get up and move around.

I have had the best results in aperture mode, shooting wide open (usually f/4). This allows me to separate the player of interest from the background. I attempt to manage the ISO setting in order to keep the shutter speed above 1/200 (to freeze action).

I have also found that I need to shoot in "AI Servo" mode; for focusing.