It is quite common to up the frequency of Humira - I'm honestly surprised your doctor is making such a big deal of it.
Both my daughters started with Humira every other week, then we moved to every 10 days and finally to every week. My older daughter stayed on weekly Humira for 5-6 years.
My younger one was a different story. She was put on weekly Humira too, but it wasn't helping enough. So we added MTX. And that made the difference - the combination was like magic for her!
We had no insurance issues getting it approved weekly. And both my daughters re-tried Humira later and we went straight to weekly the second time and insurance approved it. We even did Humira every 6 days for my younger daughter.
Are you going to a children's hospital for your son? A teaching hospital or university hospital is typically what I'd recommend - that way you know the doctors are keeping up with the research to some degree! Are you going to Boston Children's?
A second opinion is also another very helpful option. The top 3 pediatric GI departments are Boston Children's, CHOP and Cincinnati Children's - they have a LOT of experience with pediatric IBD. And honestly, given your GI did not seem to think upping Humira (which is standard in difficult cases!) was an option, a second opinion is probably a good idea.