It honestly does seem like she's an orphan, really, if you think about it.
I mean, at the very end of 'The Beginning of Rainbowland', Lady Brite says to Wisp 'You wanted a land that needed you. Now, you are its hope and light and color...'
Thus, considering this statement, it's almost like she had nothing else to lose at 'home' (wherever that is) and wished, more than anything, to be needed by
someone.
Plus, when she was first left in the Land of Shadows, she didn't seem to mind being alone.
Another thing: even though she hadn't known Twink that long, he was still her friend, but would she really have been that scared of leaving him behind when his legs began freezing if she had had someone that close to her in the past? It doesn't seem like it to me.
Then, Rainbow, being the brave child she is, would not have been so frightened or begged to go home when she was flailing in the No Return River rapids unless she'd thought it was all her fault she'd lost Twink and Starlite. I believe her devastation over thinking she'd lost the only friends/family substitutes she'd ever had caused her to panic and cry out to Lady Brite as a last resort.
Whenever Rainbow (or Wisp...before and after being given the title) talks to Lady Brite, she has the most wondrous, happy expression on her face and in her eyes (and tone of voice and how she holds herself, besides). To me, it just shows that she's never really had a protective, guardian-like figure in her life, and thus, she trusts the mysterious 'entity', shall we say, implicitly and looks up to/listens to her like any child would to a mother/caretaker.
Throughout the series, she treats the Color Kids, sprites, and all of their other friends like friends, but she also treats them like her children, in a way. Like a fanfiction I read said, the Color Kids run to her when they're scared, go to her for advice and an understanding ear, she protects them against their adversaries, and in turn, they act as children should toward their mother: they obey, care for, worry for, and love her. They exalt her and all she does, much as young children do their mothers. She takes care of them so because she's never had parents and doesn't want 'her' Kids to feel the same occasional aches with which a mother (or father) could have helped (like she sometimes does).
I'm sure I could think of some other tip-offs to probe, but I am quite out of sorts right now from staying up until 3-4 something in the morning the past two days with no sleep.
I still stand by the notion that Rainbow/Wisp is, indeed, an orphan. (As if my reasons above weren't clue enough...) If you'd like to discuss the topic further, reply, PM me, or comment on the thread I'm going to start on this toopic. I;m so intrigued, and I haven't watched an entire for months! lol. I;m somewhat surprised I remembered as much as I did from the first (for me) episode!
As another comment said, she never talks about them or noticably misses them in the show, and