Will this be bad for my teeth?

you should be fine if you brush your teeth after breakfast. if you have a bag of m&m's and eat 3 or 4 an hour until the bag is gone, or sit and eat a bowl of sugar all at once then brush your teeth. the bag of m&m's is much worse than the bowl of sugar... if you can't brush, you should at least rinse your mouth with water to rinse the sugar out