It's kind of trial and error. I would start with a very small amount
You can usually call the company you buy it from and ask them also and they can give you dosage information. The tolerance usually builds up with time. I took it myself to see how I felt and it just makes you feel relaxed and sleep better. Hope that helps.

What dose did you end up giving? I found this while Google searching for CBD information for my 4 year old.

I have been taking the cbd oil myself to calm me down it worked but like you said I built up a tolerance for it so its not working like it use to. My husband is just scared to give it to our son and we dont know what kinda dose to start at.