Help!!

So not this past thursday, but the thursday before that, Owen Grabbed the tip of my hot glue gun, I was sitting RIGHT there and it happened so fast, but it felt like slow motion anyways, he got a burn on his finger he sat in my lap for 3 hours with his finger in a bowl with cold water. My mom told me to put mustard on it sure enough I put mustard on it and never heard from him about it again. After that day I made sure to clean it, put neosporen sp? on it but he refused to but a bandaid on it. So about 4 days ago it started to look fine, and then 3 days ago it started to swell!! Does anyone know what I should do about this? Has anyone ever seen this? Don't have insurance at the moment, but will soon. (b/c of the no job thing) That's a long story in itself. Don't have time to get into it. Chad says it will be fine, i'm stressed about it 24/7. I know that if he gets a temp or a line going down the swelling its a staff infection. Haven't seen either yet, and he doesn't even act like it bothers him.