Patient was scheduled to receive the third/final Pfizer Covid vaccine (under 5).  Her first two vaccines were administered by her pediatrician's office.  The third vaccine got rescheduled.  Then pediatrician's office had flooding and is unable to currently administer Covid vaccines until they get back into their regular office and have new supply.  We scheduled appointments for Pt and her brother age 4) to receive the vaccine at pharmacy.  When called back to the private room, a technician (female, do not have name) had 2 drawn needles and a vial in a pill bottle.  She confirmed that both children were getting the third Pfizer vaccine for under 5.  I said yes.  She then asked which arm to administer for Pt.  I hesitated because they had only received vaccinations in their thigh with pediatrician.  She went to consult with the pharmacist.  The pharmacist, told them they are only trained to administer in arm and she offered to do it herself.  I accepted.  She confirmed Pfizer under 5 again and I said yes.  She checked the first needle and noticed a bend so she rejected it.  She checked the second needle and administered to Pt's left arm.  The tech went to draw another needle for brother.  The tech came back to the room a few minutes later and asked to talk to the pharmacist outside.   Several more minutes passed.  The pharmacist came back into the room and instructed me to watch Pt closely because she did not received the right dosage -- she was overdosed.  She was unable to say by how much but said the vial was not diluted by the technician before it was drawm.  The technician that prepared the needles was.   I closely watched Pt while nurse left the room again to try to figure out what happened and how much Pt received.  I called my husband (at 6:13pm) and told him to come to pharmacy and I was unsure of the severity and invredibly concerned.  Nurse came back into the room and said she thinks Pt could have received as much as 3 doses but she was still trying to figure it out.   She said they were working on getting Pfizer on the phone and told me to continue to watch her closely.  I called our pediatrician's after-hours urgent line (at 6:14pm) and left a mesage for the on-call medical professional.  I received a callback from pediatrician at 6:24pm and relayed what was happening.   Nurse came back into the room while I was on the phone with the pediatrician and she relayed over speakerphone what happened.  I was advised to contact Poison Control.  Nurse was still waiting to connect with Pfizer.  At this point, I had learned that Pt was given possible .2ml of the concentrated vaccine.  I called Poison Control at 6:32pm and spent 13 minutes on the phone.  They told me what high risk rymptoms to look out for but had thought that an immediate concern analphylatic reaction had probably passed so we did not need to go to ER.  He told me what symptoms to look for overnight and when to go to hospital or call pediatrician.   Poison Control then spoke with Nurse as they were making a report too -- my report came in first.  Our pediatrician's office called back again at 7:13pm to check on Pt's status.  They said to follow advice from Poison Control and keep in touch if she started developing any concerning symptoms.  On the low end of the spectrum, they expected her to have amplied effects from the vaccine -- extreme arm soreness, fever, chills.     We asked to see the vial because it was still very unclear how much Pt received and we wanted to verify that it was at least the right vial.   After some time (10-15), Nurse brought the vial back along with a color coded chart that revised the administration instructions for each Pfizer vaccine (under 5, 5-12, adult) -- my husband looked at it more closely than me as I was observing Pt.  Nurse said the vial had .7ml of the concentrated vaccine and it was support to be diluted with 2.2ml of saline before it was drawn.  Supposedly that is supposedly to give you 10 doses.  The numbers didn't seem to add up to Nurse or my husband because adding 2.2 to the vial would overflow the bottle.  Nurse agreed that something was off.  My husband was researching online and found reports where the vial was .4ml frozen so once thawed we thought it would be closer to .3ml not up to .7ml.  Nurse was confused as well so this was more alarming to us because we couldn't ascertain just how much of a dosage Pt was given.    Nurse relayed that Pfizer was not really helpful because it was not administered properly so they could not offer guidance and we should follow Poison Control recommendations/guidance.   Nurse confirmed that internal reports were being done.  She was going to try to find the information packet that comees in the bag of vials --- she admitted that they throw them out because the information is supposed to be available online but she was not able to locate it online and was receiving error messages.   My son would have received the same overdose had there not been an issue with one of the needles.  I do not know if any prior children were overdosed.   They offered to do his vaccination and I rejected it.  I asked them to correct his vaccine card because they had already written on it but he did NOT receive it.   Poison Control followed up on Pt's status around 8:23pm.   They advised me to file this adverse event report.   We monitored Pt closely during the night -- checked on her every hour.   She started developing a fever this morning when she was checked at 8:30am.   Her temperative has gone up another 2 degrees is at 102 now.   Being that she's 3, she's still somewhat limited in conveying information but has extreme arm soreness, asked to stay in bed with me and deesn't feel good.  She also appears to have chills and had little interest in breakfast (she did eat a good dinner around 8:15pm last night when we got home).   I consulted with the pediatrician again around 10:30 regarding providing motrin/tylenol for discomfort and am trying to get her to start that.   The most  "unclear" feedback I am able to get is that they hope she will just have amplified side effects today and tomorrow.   I hope so too.  If there is additional information I can provide, please let me know.  I do not know what will happen as a result of this adverse event but the administration of this vaccine at this location must get action.   The technician was admittedly negligent and I intend to pursue follow-up recourse as I assume they must have some license or certification.  The lack of clarity about the dosage and measurements is very concerning.