Childlings: Mortal children can have a very black and white sense of what is or isn't fair, but when a Rusalka childling says "that's not fair" there is good reason to be afraid, for the childling might very well do something about it if the adults in their world won't. For this reason, Changelings are learning it's very important to give Rusalka childlings guidance on patience, and forgiveness. They are still kids, of course, and for all their huffy sense of balance, can be distracted by fellow playmates with offer of a game or the like.
Wilders: While Rusalka are not bound to any specific shore or river, it is when they are wilders that they are willing (even eager) to travel from the waters they know to the ones they don't. In school situations they can often be the social justice types, but are just as likely to reign in the excesses of bullies by means fair and foul. Romance with a wilder Rusalka can be playful and frolicsome, and then get rather intense and dramatic as their paramours must account for their slips at an age when everyone makes mistakes. Like the rivers they often roam, a wilder Rusalka can seem very at ease, almost lazily content one day, then the next break into a flood of indignity that there is injustice that must be fixed and how is it no one else has seen this?
Grumps: Rusalka grumps may look young for their age, but their wisdom, hard won through mortal and fae life both, has taught them how complex true justice can be. They are in some ways, more open minded, but the complexity sometimes robs them of the passion they had and, can be a dangerous path to apathy. Rusalka grumps can be more prone to withdrawing from the world, and often become more territorial about specific river sides or marshes in a 'get off my lawn' kind of way.