There are some people who just don't have symptoms. It's very variable. My daughter was diagnosed at 16 and her only symptoms were mild constipation and abdominal pain. And weight loss. NO diarrhea or bleeding. Some kids present with only weight or growth issues and NO gut issues at all. Some kids are completely asymptomatic - no symptoms at all.
The goal with IBD is to control inflammation to prevent complications like fistulae, abscesses, strictures. To prevent surgeries. You need your small bowel to live, so you definitely don't want to have multiple resections if you can help it.
All drugs with side effects but you have to look at risks vs. benefits. Serious side effects with biologics like Humira are very rare but serious complications due to untreated inflammation because of Crohn's are not.
As a parent, I worried a lot before I put both my girls on biologics. I spent many sleepless nights agonizing about whether it was the right choices. But at some point the disease becomes scarier than the medications. Both my girls have been on biologics for 8-9 years with NO side effects at all. They have been life-changing medications for my daughters.
Good luck with your decision.