Does it have to be superheroes ?
Well, frankly, no.
I guess it all depends how you define superheroes.
With the character I've been developing - Kid Prospero, he's a magic user who will wear a colourful costume but it wont include a mask and I envision it being more like a bright jacket and a t-shirt with 'K.P.' on it.
But that being said, it should be a concept that fits within a superhero-style present day shared universe.
Why do a children's comic? Personally, I think a new super-hero comic would be cool for adults or "older kids", but I don't think it cracks the kids' market. Youngsters coming in to anything tend to play it "safe", go with established brands or "entry drugs"...like Batman, Superman, Spiderman and all of the Big Names. I like your idea, I just think it would be more successful for a slightly older - and more daring - audience. That's just my two pennies rubbed together, though. You all may prove me dead wrong.
Why do a children's comic? Essentially, because there is a lot of stuff aimed exclusively at an adult readership now. But perhaps 'kids comics' is the wrong description. What'd be great is a comic book that is all-ages. Which adults can pick up and enjoy but is still suitable to be read by children as well.
And yeah, a comic book for older kids would be great too. I see no reason not to aim at different age ranges. For instance, we could have a group of books aimed at kids 6-12 years old and another group for 12 years and older.
What makes something all-ages is less about it being unsophisticated and more about it including bright colours, a lack of real guns with an absence of swearing and other harsh language.