It will take more like 50 at bats and he won't play every game. You figure he'll average 4 AB a game, that would be 13 days. I'd expect him back for the Baltimore series in early May.
Fenway Park has a family friendly atmosphere. If you're really worried, just avoid the bleachers but I don't think you have anything to worry about. I've seen fans of opposing teams act like fools and draw as much negative attention to them as possible and all they get is jeering in return. At worst you'll get a piece of pizza thrown at you.