Yeah, It seems like a pretty common thing for a child’s fingers to find their way into a parents mouth. Sometimes my daughter just jams her hand in my mouth for no reason at all.
An hour ago I had no idea what caries were so did a little looking and from what I saw it is the combination of bacteria and food staying in the mouth too long that cause tooth decay. Sticky foods are worse so I suppose because candy is stickier than most food that it would be worse for the teeth.
One site suggested rinsing your child’s mouth with water after they have candy to dilute the residue left on the teeth. I’ll have to keep this in mind because I live in a pretty friendly neighborhood and the neighbors love to give my 2 1/2 year old daughter candy