I have about 5-6 girls (out of around 30 track athletes), both sprinters and distance runners, who exhibit hip pain in either one or both sides when training volume increases. When training frequency increases, more kids get into same trouble.
Usually b4 they get into trouble I have already spotted potential areas of weakness and poor posture and/or technique in at least a couple of them, even when they are simply walking or standing around. They also appear more listless than usual. Usually this coincides with too much stress at school, esp when the school has arranged too many activities in a short period of time, or when they have a series of tests coming up.
There are also girls who are required to attend extra lessons after school either as remedial lessons or make-up classes to catch up on the syllabus, and this not only increases mental stress on them, but also increases the amount of time they remain in a seated position, which usually leads to some measure of slouching. This can affect their back, neck and groin area a lot, even if they are not athletes.
Also watch out for kids who are involved in other sports. I have girls who are ballerinas, gymnasts, swimmers, dancers, etc and these are activities which make great demands on the hip and lower back regions. They are usually VERY flexible girls (180 deg straight leg centre splits!)but still they experience hip trouble in running workouts. It seems to be a case of overuse and fatigue.
The situation I face is such that when these kids get to training after an exhausting day (or days) at school, they are mentally too tired to control their movement efficiently. This can lead to poor running form and therefore hip pain. Physically, some of them are too spent to push their bodies even optimally, even when they actually feel fine initially. But as athletes they have such a strong mind and will that they often block out any discomfort quite effectively and just train thro it all.
I would agree with Runningart2004's post on the stretching exercises u could get yr kids to perform. His recommendation on the gluteal and core exercises are also very relevant. Many kids fail to activate their tranverse abdominus (TVA) when they run and this results in the trunk resting entirely on the pelvis when they stand or run. This places a lot of stress on the hip flexors, iliotibial band and even the hip external rotators (esp for those who like to stand on one leg). Tightening of any one or all of these areas can lead to hip pain.
Also if yr TVA is not activated when u run, the weight of the trunk resting on the pelvis inhibits hip rotation during stance phase, when the foot lands on the ground at ball of foot and is on the way backwards. The iliopsoas is at this point operating in a compressed position and a shearing force is applied backwards against it as the leg swings backwards. If no hip rotation occurs at this point, the runner usually tries to get propulsion by pushing off hard with the foot and hyperextending the thigh area. Imagine trying to drive the whole leg rearwards while 'locking' the leg at the hip joint area. U r virtually holding yr iliopsoas rigid while trying to rip it apart rearwards with each stride!
Having loose hips when we run is paramount. But stretching will only get us so far. It is useless being flexible only to put yourself in a position that inhibits hip mobility. All that flexibility will not be in use at all, and injury will still result.
The challenge is in getting the kids to understand and consistently apply good postural habits when they run. As I've mentioned earlier on, some of them are simply too tired after school to execute the correct postural cues, even if they really want to. The sad reality is that some of the physical problems our kids face are actually related to the stresses of modern living. (Maybe that's why the Kenyan teenage girl is running 1.54 800m at Beijing and there are no Americans in the women 800m final even! The less developed nations simply do not put so much stress on their kids in school as we do. They do not need to "keep up with the Jonses" like more affluent societies tend to do. But I digress.....)