I just responded to your dosing and safe herbs question in the Internal Preparations section, but for your specific situation, I can suggest a few herbs however we aren’t able to really give specific health advice on this forum, so I will link you to the Pacific Rim College student clinic (which is free), where you and your son can get personalised support. I highly recommend in this situation. There is so much that can be done here and I hope that you get the support you both need. https://pacificrimcollege.janeapp.com/#/phytotherapy-instructor OR https://pacificrimcollege.janeapp.com/#/phytotherapy-student
Some short suggestions are to first and foremost look into his diet and soaps (consider laundry-even your laundry if you use different soaps for the both of you, dish and bathing soaps) that may be triggering a reaction. This can form at any point and is often a cause. Dry air and heat can exacerbate the situation as well.
Herbs that might be of support internally: milk thistle, dandelion, nettle, echinacea, maybe cleavers and burdock-but starting at very low doses)-pay attention to his bowel movements as well. How are they?
Externally a salve with plantain, calendula, lavender, rose, sometimes comfrey, self heal, chickweed, marshmallow, yarrow….the list here is long and you would have to choose out of these based on how the eczema is presenting, is it wet and weepy? Dry? Hot? etc. As you’ve been learning each herb has slightly different profiles and one may be more helpful for your sons eczema than the other. E.g. calendula is quite warming and dry, marshmallow is moist and cooling
I wish you and your son the best, seeing a practitioner will be the best thing you can do at this point.