As a kid, I remember going in to see the family doctor to get the "OK" to play school sports. I remember that he would check my blood pressure, listen to my heart and lungs, do a few quick tests, and say that I was good to go. I remember it being not such a big deal, but he was checking for some important information. I do, however, remember that he didn't do so much with my posture or spine. I'm guessing the reason would be that he wasn't qualified to to so.
Being in the chiropractic field as I am currently, I realize how important it is for kids to get their posture and spine evaluated prior to engaging in any sports. The sad thing is that most kids don't get their spine evaluated. I believe that if more parents were to bring in their children for a spinal evaluation, some injuries could be prevented.
If a child's skeletal system is not properly aligned, there is going to be an undue amount of stress on areas that aren't used to having as much stress from sports. For instance, baseball players typically bat from one side of the plate, which means swinging and twisting only one way constantly. If there is a misalignment of the pelvis or spine, the body won't be able to move like it's supposed to. That can lead to a higher propensity for injury. Or, for a sport with a lot of running like soccer, any misalignment of the spine or the legs can possibly lead to hip, knee, or ankle injuries.
Many professional, and even college, sports teams have their own personal chiropractor on staff or at least within reach. This tells you that the best of the best know how important it is to keep the spine and body in line when performing physical activities such as sports.
So, if you're bringing your child in for their yearly sports physical with their family doctor, I would highly recommend and even urge you to bring them in to the chiropractor. It is important to make sure the body's organs are funtioning correctly, but it's equally important to have their spine functioning correctly.