YTA
Annual odds of:
So tell me that you inspected her house for proper storage of all household chemicals and cleaners and also emailed the parents about any potential poisoning issues you found. If you didn't do that also then you ruined her son's party because of your entirely non-rational fear.
It wasn't your concern since it isn't your party and isn't your home. If they are concealed carrying, legal, law-abiding citizens then it isn't any business of your other than your personal feelings towards the issues.