Despite the popularity of creatine among young people, there has been very little research conducted in children under age 18. Of those studies, a few have suggested a positive effect but the overall evidence is inconclusive. In one study, teenage swimmers performed better after taking creatine; in another study, it helped high school soccer players sprint, dribble, and jump more effectively.

Gualano, B., de, Salles Painelli, V, Roschel, H., Lugaresi, R., Dorea, E., Artioli, G. G., Lima, F. R., da Silva, M. E., Cunha, M. R., Seguro, A. C., Shimizu, M. H., Otaduy, M. C., Sapienza, M. T., da Costa, Leite C., Bonfa, E., and Lancha Junior, A. H. Creatine supplementation does not impair kidney function in type 2 diabetic patients: a randomized, double-blind, placebo-controlled, clinical trial. Eur.J.Appl.Physiol 2011;111(5):749-756. View abstract.

All you need to know about low creatinine levels Creatinine is a waste material in the body, and low levels can suggest a shortfall in liver function or activity. This MNT Knowledge Center feature looks at low creatinine levels., as well as information on what creatinine is, how it affects the body, and how to increase low creatinine levels. Read now
A: Let your symptoms be your guide. A slight sore throat or runny nose may require you to back off for a day or two but don’t confine yourself to your bed and assume the worst. However, you must also remember that prolonged, intense exercise can decrease immune function and make you more susceptible to bacterial and viral based sickness so it's equally as important to listen to your body and respond accordingly.
According to the two meta-analyses on the topic, creatine significantly increases power when supplemented in both sexes over a period of time up to 8 weeks, during which improvement over placebo is maintained, rather than being enhanced further. The rate at which power is derived from a resistance training regimen appears to be up to 78.5% greater with creatine relative to placebo, and in active trained men who are naive to creatine, this can be quantified at about 7kg for the bench press and 10kg for the squat over 8 weeks.
Change things up. After six or more weeks of consistent strength training, which is about the amount of time it takes to start seeing improvement in your body, you can change your routine to make it more difficult. Lifting the same weights for the same exercises every week will keep your body in the same place. You can modify weights or repetitions, choose different exercises, or change the order in which you do them. You only have to make one change at a time to make a difference, although more is often better. 
If there are any benefits for swimming performance from creatine supplementation, they appear to be limited to a 50 meter sprint or a handful of 50 meter sprints with short intermissions. Excessive sprinting (over six sprints with short breaks) or too long of a break (five minutes rather than two) seem to not be associated with the benefits of creatine supplementation.
Key point: Past a certain number of sets, the marginal increases in protein synthesis NO LONGER outweigh the cost of doing more sets. If 8 sets of chest exercises produce 95% of possible muscle protein synthesis… then it makes very little sense to do ANOTHER 10 sets (like most chest workouts) to try and inch out the final 5% of stimulation. Those extra 10 sets are simply damaging your muscle unnecessarily and impairing your ability to recover.
Some ingredients found in dietary supplements marketed for bodybuilding or performance enhancement—such as whey protein, creatine, and caffeine—generally aren’t associated with any serious safety concerns (when used appropriately). However, they still have the potential for side effects. Before you take any dietary supplement, talk to your healthcare provider. You also can read the articles below about some of these ingredients:
Creatine (/ˈkriːətiːn/ or /ˈkriːətɪn/[1] is an organic compound with the nominal formula (H2N)(HN)CN(CH3)CH2CO2H. This species exists in various modifications (tautomers) in solution. Creatine is found in vertebrates where it facilitates recycling of adenosine triphosphate (ATP), the energy currency of the cell, primarily in muscle and brain tissue. Recycling is achieved by converting adenosine diphosphate (ADP) back to ATP via donation of phosphate groups. Creatine also acts as a buffer.[2]
Synthesis primarily takes place in the kidney and liver, with creatine then being transported to the muscles via the blood. The majority of the human body's total creatine and phosphocreatine stores is located in skeletal muscle, while the remainder is distributed in the blood, brain, and other tissues.[17][18][20] Typically, creatine is produced endogenously at an estimated rate of about 8.3 mmol or 1 gram per day in young adults.[16][17] Creatine is also obtained through the diet at a rate of about 1 gram per day from an omnivorous diet.[17][18] Some small studies suggest that total muscle creatine is significantly lower in vegetarians than non-vegetarians, as expected since foods of animal origin are the primary source of creatine. However, subjects happened to show the same levels after using supplements.[21]