This is the rating scale that can be used with kids. It's simpler and isn't as wordy as the one I use. For example, all it has to say it a short sentence about how they feel and what they can do to calm down (Anxiety Level 5: It is out of control. I need to be alone.) All these will be different for each child.
I'm on the higher-functioning end of the autism spectrum. This is something I use with people to help me describe my anxiety/frustration level. Each level describes my body language, how I'm feeling, and what I need to do to calm down. All I have to do is tell them what number I'm at. A simpler one can be used with children as well. I have that one up too. It can also be used for a number of other things like noise level in a classroom, anger, when feeling sad, etc.