We pretty much use the same things!
A staple around here is to add goji berries, chia seed, spirulina, chlorella, and aloe vera juice. We also often times add tahini or sesame seeds.
As far as I know there are no "nutritional guidelines" for kids. Pretty much any raw whole food that's good for you is good for your kids. Do limit wheatgrass though as it contains a relatively high concentration of alkaloids. Also go easy on spirulina if you use the dry form as we have witnessed our son have a hard time with it on his system when he was younger.
Continue to keep the amounts small as you try new things, build them up slowly and pay attention and things should be just fine.