I started my 2 y/o dd on coconut oil when when she was one. She really did great on that, went up to 75th percentile for weight from 25th. I also give her a probiotic daily and add sea salt instead of refined salt.
I did not use fish oil, I used flaxseed oil instead but then I read that it was not advised for kids under 3 so I stopped for now and switched her to tumeric (curcumin) powder that is also supposed to fight inflammation.
I did run the coconut oil by dietetician, but just to make sure it is not harmful. At my hospital they are sceptical about these things, so would not expect any advice there, but your clinic might be different.