I know for certain that First Aid at the WDW Theme Parks and Water Parks are staffed by Registered Nurses.
I am also an RN.
Registered Nurses in each state practice under their state’s Nurse Practice Act, which can vary a bit, but are generally very similar.
The Nurse Practice Act identifies which things the RN can do independently and which need to be under the direction of a Licensed Independent Practitioner (Physician, Advanced Practice Nurse, Physician Assistant).
Independent practice includes things like observation, assessment, intervention, health teaching, etc.
Registered Nurses can also administer medications and treatments prescribed by an Independent Practitioner. These are often covered under standing orders, which are lists of treatments or medications to give under specific circumstances.
A couple of the specific things I know for sure they have standing orders for are allergic reactions, sunburn, illness related to sun/heat and nausea.
The injection that musicmom was at First Aid for could possibly fit under one of their standing order sets.
They have over the counter medications that don’t require a prescription; they are most likely to ask if you would like them, but not actually administer them.
Most of the time, we are going to First Aid either to do my daughter’s catheter or to give her medication. I do tell the person at the desk what we are doing so that I get an appropriate room/space. Almost always, I am asked if I need any assistance from the nurse or anything from them.