momofchild,
Welcome to the forum.
So sorry about your son having been diagnosed with UC.
It's bad enough when we, as adults get it, but little kids is tough.
You've gotten some great advice here already.
I just want to caution you that a "healthy 100% natural diet" is great for many, but may not cut it for UC. No junk food, and HFCS is great, but if you're still giving him dairy and gluten, which for many IBDers is a real problem, just reducing those intakes and eliminating them may make a huge difference.
How about starting a food journal to see what correlations develop?
In my experience I have found that diet modification, such as going gluten and dairy free, going PALEO ( grass-fed animal products), increasing omega 3's, adding vitamin d3, probiotics, slippery elm powder, l-glutamine, and LDN, low dose naltrexone has enabled me remission.
And if you are interested in seeing how it may fit into your treatment of your son, there are things IMO that you can control, which will have a direct impact on your disease, the symptoms you experience and their severity.
I was able to control my UC into remission through various supplements, probiotics, diet modification, and LDN , low dose naltrexone.
For more info on the protocol which has put me into remission, please go to this link: https://www.healingwell.com/community/default.aspx?f=38&m=1666318 , and look at the 11th post.
I hope you feel better and let us know how we can help you.