Hi and welcome!
I'd check out the parent's forum if I were you -- there are several parents there with teenagers with IBD. CCFA has a great presentation that talks about the risks and the benefits of various IBD medications:
http://programs.rmei.com/CCFA139VL/
I can tell you we agonized and agonized about putting our girls on medications, but at some point, the disease became scarier than the meds. They are both on biologics plus immunomodulators - Methotrexate for the older one, and Imuran (similar to 6MP) for the younger one. The difference these medications have made in their quality of life is incredible.
My younger daughter has not had any issues with Imuran - some nausea when increasing the dose, but really no other side effects.
There is a cancer risk, but it is very small. I will say that more and more doctors seem to be using Methotrexate more than 6MP for kids, because 6MP/Imuran are slightly more risky. In my younger daughter's case, she tried Methotrexate but could not tolerate it, so we had to use Imuran.
My younger daughter's last set of scopes showed that all the ulcers in her colon had healed and that there was just some mild inflammation in her small bowel, after 8 months of Remicade and Methotrexate (this was before she started Imuran). In fact, the doctor said her colon looked "beautiful" which she is very proud of :lol:.
With untreated Crohn's, the risks of strictures, fistulae, abscesses etc. are high but with medications, the disease can be controlled. And many kids do not have side effects at all with medications. Your child will also be monitored very carefully to make sure he is tolerating 6MP - usually they do weekly or biweekly bloodwork in the beginning.
Good luck with whatever you choose!