There are new resources being developed all time to help children manage anxiety. For individuals, I begin by assessing how big a concern anxiety is for them. I do this a variety of ways but one all the students seem to favor is selecting the stone that represents the amount of discomfort their worries are currently causing them daily. I have a small pebble, a 1-2 inch rock, and a 4-5 inch rock that I keep on my window sill and bring out. I say, "you could have a little anxiety and it fits in your pocket and you only notice it occasionally, a medium size rock in your pocket that you would notice every time you moved, and a heavy rock that would weigh down your backpack." Once I know how big a problem the child perceives their anxiety issues to be I start assessing their coping tools. What have they tried so far that works to reduce their anxiety when they are stressed? What did not work? If I do see a student for ongoing short term counseling we set a goal to reduce anxiety and quantify it (for K-1 to make it a pebble and for grades 2-5 to reduce it from a __ to below 5 on a 10 point scale). I have found that students who are highly perfectionist or compulsive do not like groups and will only agree to individual support.
If possible I try to have most students with anxiety issues participate in small group counseling. It has many advantages and students help one another as much as I help them. For groups, especially in grade 2 my students love worrywoos The books in this series are great and the website offers some good materials to create activities.I have done a whole group based on the worrywoos. For more resources check out my pinterest/worry--anxiety-stress board. Some of my favorite picture books on anxiety are: Hey Warrior, Caterpillar's Wings, The Huge Bag of Worries, and The Worry Glasses. I generally teach a strategy each session and provide members opportunities to practice (calming exercises, deep breathing, mindfulness, etc.)
Stress is so pervasive in my school I teach a class lesson on techniques to reduce stress in grades 3-5. I think this further helps normalize anxiety issues and gives all students a few tools to self-regulate when experiencing normal stress. Since we use Second Step I use their lessons in the classroom.