Kitt's question about your grandson's age is very pertinent. I'm also curious, was your grandson having any suicidal ideations prior to his taking the antidepressants? If these thoughts are completely uncharacteristic, talk to your doc ASAP! If the thoughts aren't alien just uncomfortable, the wellbutrin could be just starting to work, and he is still depressed. It is still important to call your doc regardless. There are all sorts of other anti-ds out there, hopefully he can find one that doesn't exaccerbate his situation. I've been taking Wellbutrin on and off since I was 24, and I never experienced any thoughts in my brain that weren't there previously.
He might also benefit from being in "talk therapy" if he isn't already. Relying solely on a medication is never the best way to fight off depression. If you can, try to get him to start exercising every day, as this has been proven time and again to help fight off depression. Keep us posted on his journey to wellness, and don't forget to take care of yourself as well.
Diagnosed w/ moderate UC in May '06, had symptoms for years prior to dx - currently flaring
Suffered from depression since I was 19
Asacol, Florastor, VSL#3, Wellbutrin XL, Prozac, multi-vitamin, and fexofenadine for allergies