I agree with imunique. Such a small amount of milk chocolate isn't all that dangerous. Obviously you should never feed it on purpose but it happens. Things get dropped and dogs eat anything that hits the floor. Dark chocolate and especially Bakers cocoa is deadly to dogs and can cause a heart attack. For that, don't even take the time to read the internet, call the vet immediately. But milk chocolate candy will usually only make them sick to their stomach. Max is big so the quantity is no comparison to your little puppy. But he once stole a whole box of chocolates off the kitchen counter and he got really, really bad diarrhea. All the vet told me to do was to feed him white rice and to keep an eye on him.
Your dog will be fine as the above posters mentioned. The toxic substance in chocolate is theobromine, and the toxic dose is 100-150 mg's of theobromine per kg of dog. Milk chocolate has 6 mg's per ounce in it, semi-sweet chocolate has 22 mg's per ounce, and the worst is dark chocolate, or baker's chocolate with 35-45 mg's per ounce. If you know your dog has ingested any amount of chocolate,you should immediately induce vomiting by giving hydrogen peroxide,and run to the vet. Milk chocolate (a good chunk) will usually result in diarrhea, depending on the size of the dog. The other chocolates are a different story, far more dangerous, and not to mess around to see what's going to happen. I had an old Springer Spaniel who would look for easter eggs with the kids, and as they dropped them, she would grab them and go and bury them. She lived to the age of 17 though, my faithful old mutt.
She should be fine. One peanut m&m should do no harm but my uncle left a bag of m&m out and his cat maybe ate 5 m&m and she had trouble going 2 the bathroom. So do not leave a bag of m&m open cuz cats r curious. Have u every heard the saying "Curiousity killed the cat".