Hi and welcome!
My daughters also hated Humira at first. They were older than your son though (teenagers) so once they figured out it helped them feel better, it was totally worth it to them.
There are definitely some tricks you can try to lessen injection pain. Some parents add Lidocaine to Humira and inject a mixture of both. I'll tag my little penguin, since she did that for her son for years - she can explain how to do it and get your doc on board.
You can try something like Buzzy, but that really helps more with the needle poke and it's the medication that burn with Humira. But my older daughter (who is still on Humira) says it does help a bit. Here is a link:
https://buzzyhelps.com
The other that REALLY helped us was distraction. You can ask him open ended questions to distract him. Or have him play a fast paced video game so he is focusing on that for the shot. We did the shot while my girls watched TV, which worked for us, but really the more focused you can get him on something else, the better it will work.
Lastly, some parents have had success with taking kids to see a psychologist to help deal with the shot. There are coping strategies that he could learn - breathing, visualization etc.
There are very few meds for Crohn's and even fewer for pediatric Crohn's, so you don't want to lose Humira as an option unless you absolutely have to.
The other thing Ron was talking about is the new formulation of Humira - they have actually reformulated it to remove the ingredient that burns. The new formulation has been available in Europe for quite a while now, and many members on here say it's MUCH less painful.
It was supposed to be released some time this summer in the US. I heard that AbbVie wants to use up the old formulation of Humira and then they will release the new formulation. So probably pretty soon...
I'll tag some more parents who may have ideas:
Clash
Pilgrim
Farmwife
Jenn