I have taken pictures in the gym before but what I find is that many times the kids up close are out of focus and I don't like how that looks. That is why I was wondering if I needed a different lens. We have a stage and where the kids' rows start is only about 5-6 ft. away and I can't go back any farther without getting on the stage and I'd rather be at eye level. The lighting (fluorescent) isn't great but most of the time I can keep my ISO at 800 or lower when they are on the gym floor. If they are on the stage that is another story.

I know you are all knowledgeable and I need your help with choosing the right lens. I am a teacher and take tons of pictures at school. Inside and out. Friday's we have a morning meeting with all of our students and we do a number of different activities and I try to take advantage of those times when we have all of the kids together. I have the Canon T3i and need some suggestions. I would like a lens that I can take pictures that will give me a good depth of field as well as sharp near and far and side to side so I get a large number of the kids in the pictures. Sorry for my lack of technical terms. I have the standard kit lens that came with my camera. Do I use it and just use f22 aperature with a higher ISO since the lighting isn't great or is there a lens that would work better for my gym situation. I hope I am not offending those of you that have "been there done that" when answering this question a million times.
I also have the Canon 24-70 f2.8 IS lens. Is this a better choice? If so what settings would you recommend with this lens.
I am envious of all of the knowledge everyone has on this site and was hesitant to ask because I didn't want to expose my lack of knowledge. But, I want to improve my photos and know this is the place to go and learn from the best.
Thanks in advance for your help.

I have taken pictures in the gym before but what I find is that many times the kids up close are out of focus and I don't like how that looks. That is why I was wondering if I needed a different lens. We have a stage and where the kids' rows start is only about 5-6 ft. away and I can't go back any farther without getting on the stage and I'd rather be at eye level. The lighting (fluorescent) isn't great but most of the time I can keep my ISO at 800 or lower when they are on the gym floor. If they are on the stage that is another story.

OK, they sit on a flat floor, the stage is 4' high, just about right to shoot at a slight down angle if you sit on the edge of the stage and then have them all look in the direction of the camera and use aperture of f11 or f16 and focus on the row that is from 1/3 to 1/2 way into the depth of field. If the shutter speed is too slow at f11 or f16 use a fairly powerful external flash. (Could those blinds be opened to get in more ambient light? Or are they on the wrong side to light their faces?)

Kids sit on the floor. Many times we get them up to do different movement type activities. In those pictures I usually change the setting to Sports because I figure that is a better setting for when they are moving. I've tried TV and not had very good results at all. Not sure what I am doing wrong there. I know that the shutter is staying open to long but when I've tried to increase it I still don't have good results. Maybe I am not increasing it enough. Tried a couple of times to up the ISO but then the pictures were to grainy. Decided at that point to stick to one or two modes because I was getting confused on what I had tried. Everything moves to fast for me to take a notebook in and write down what I've tried. We only have about 20-30 minutes on those mornings so we move pretty fast from activity to activity.