I work with a decent amount of kids from 4-20 years old. You might think that there is a big difference there but if you are still growing as far as I am concerned you are still a kid and no don’t mean wider. Here is my 2 cents on Growing / Growning Pains as you grow your bones increase in length and as that happens muscles go from being loose and a bit uncontrolled to snug or tight do to the added length and they can pull joints into directions that they are not designed to go. So using hamstrings as an example you are dealing with a muscle that attaches at the back of the pelvis by the bottom of your butt and runs down and attaches to your lower leg or tibia. I am not being super technical here so chill out anatomy buffs.
So this muscle has to get longer as the femur grows and as the tibia grows. So two bones growth plates directly affect the tension / length relationship of this muscle to the body. So while some kids complain of tight hamstrings many more complain of knee pain in the anterior or front of knee. Many times the problem is not where the pain is and taking the pain away only decreases the likeliness of good healing.. So they Ice and Heat and wrap and needle and get therapy on all different parts of the knee when working on getting normal length of hamstring and good quality muscular balance is much more important than symptom care or in other words getting rid of the pain. Most of the time poor stretching techniques and poor mechanics are the underlying areas of interest to me. Most of the kids I have treated for knee pain have poor posture, bad leg positioning, being “pigeon toe” or bow legged or knock kneed and many have poor foot to lower leg alignment so tension in calves and and muscles of the lower leg are the actual culprit. Again searching for symptom care instead of healthcare is in general a really bad idea.
If your kid suffers from pain, in knees, feet, ankles, hips you might want to have a professional take a good look at their overall positioning and mechanical technique before you start giving them silly drugs like Ibuprofen and painkillers. They are rarely the correct answer to this question.