C.-
Sorry this is so long...
Don't panic! That's my first advice.
I have a son with severe ADHD. His kindergarten teacher first noticed some things so she gave him a baby brush to rub his skin (sensory) which helped him focus and the brush was so soft it didn't hurt him. I would bet your daughter was rubbing her arms because it allowed her to focus or she had some anxiety. So get her a nice soft brush or cloth or something to have in her desk and she can use it to focus or if she's anxious.
Next, make sure you have a very good behavior system in place at home for both kids. That way you can discern if the behavior is about testing limits.
Then, I would limit caffeine, sugar, treats etc. Some parents will pull all kinds of stuff assuming allergies (which can cause similar behaviors to ADD/ADHD).
While you're doing all this at home, set up an appointment with both teachers and special ed or principal so you can start a full battery of tests. It will take a month easy and another month for the report so you want to get started on this right away, so your game plan is in place for next year.
Contact your pediatrician and set up appointments and start with the check list for ADD/ADHD. You will fill it out, teachers and others that are close to your children or spend a lot of time with them. This check list allows the pediatrician to see if the behaviors are isolated to certain situations. I was told that if the behaviors were not pervasive, then it was unlikely to be ADD/ADHD. This is what you need to start.
Also, it is important to know that ADD/ADHD diagnosis can not be given by anyone other than a pediatrician. Teachers cannot make the diagnosis, but they may see some of the signs. Should it come down to your child/children having an ADD/ADHD diagnosis, you have many different options for treatment including dietary supplements, food restriction, therapy, counseling, behavior modification, as well as medication. My son is on medication, because the changes were not dramatic enough to help my son when using alternative treatments. It took me two years to come to that point.
As for the sensory issues, I would consider booking an appointment with an Occupational Therapist that specializes in sensory disorders. She/He will help you better understand your children. My son is a sensory seeker in everything. There are sensory avoiders and mixed. I know very little about this other than what I was told about my son. What I did find was that the medical community was not particularly open to a diagnosis of sensory disorder. So that usually means issues with insurance paying for treatment. My son, now 11, just stopped chewing on his clothes about a year ago, but for the life of me I can't get him to stop chewing his nails and cuticles. Before either of those behaviors he would suck his thumb. It was/is a behavior that allows him to focus on what he's supposed to: school, baseball, church, etc.
Good luck, C.. Blessings,
S.