Obviously it's not as healthy as, say, a banana but simple popped corn, no salt, no butter, not cooked in oil, is a "healthy" alternative to crisps isn't it? I've just got a popcorn maker (it's fab!) and am using it when DSs (6 & 4) want a snack - they think it's fun.
And before you all jump on me, DS2 will not eat any fruit and it's not through a lack of trying. Might see if he eats sunflower seeds actually...