I got 5 Moonkin Hatchlings following me around for the next 5 days because of the Moonkin Festival. It looks like they're doing an animation sorta like Moonfire during fights - are they actually helping me, or are they just for show, as it were?
Just like most micro holiday rewards they're just for show (and totally cute) and are only there for a limited amount of time. The title Adventuring Instructor will go away as well as soon as the buff wears off.
The only thing the moonkins are good for is their interaction. They tell you how awesome you are, but don't grant anything useful for combat (although they do "fight" with you with their little moonfires they don't do any damage - it's just the animation). Also you can /dance with them and they'll start dancing as well.