WoWDB

A few things to note for people who want to get this little guy:

1. The Wanderer's Festival is affected by the 5.1 time changes. All realm activities, including this one (and fishing contents, etc.), are based on PST, so that means the Festival starts at 9pm PST and ends at 12am PST on all servers (save Oceanic).
2. I recommend using a targetting macro for this. As a note, I used /tar Wanderer's Festival Hatchling. I originally was simply using /tar Wanderer, but the lanterns that spawn in the water are named Wanderer's Festival Lantern, so they were picked up by the macro. Binding a key to interact with target (through the actual menu, not through a macro) is what enabled me to get into battle with a hatchling before I closed the full distance.
3. The hatchling I fought was 25 (though others mention they are 23), so come prepared with enough high level pets. They are aquatic, so they're weak against flying pets. Only 3 spawned at the start, right after the fireworks.

I would also recommend taking some time to check out the Festival itself! The NPCs and the lore were very enjoyable.

Only available during the Wanderer's Festival which happens every Sunday from 9-11pm server time.

It's at Turtle Beach, just NE of The Incursion in Krasaran Wilds near the statue of Liu Lang (72,30), and you gain the Wanderers, Dreamers, and You achievement for attending the opening or closing ceremony.