Why do they love the things they love?

So I read in one of my Greener, Organic Mommy Mags that avocado is a great healthy snack for kids. I don't remember exactly why they said it was so good for them, but with most things I read about or hear about that are good for them, I hear its good retain that part and go with it. Carolina and George were way past their adventurous eating stage to even consider trying it. It was just way to "green" for them, but not Laney she will try almost anything or at least at the time I let her try it she would. She has since decided that she doesn't want to eat anything except string cheese, popcorn, pop tarts and grilled cheese. Oh and just about any kind of chip she can get her hands on. Anyways, I got her to try it back then and she LOVES it. I cant scoop it out of the skin fast enough. I couldn't keep enough on her plate. She ate two thirds of the whole avocado. I barely had enough to make the guacamole that I bought the stinking thing for in the first place. Oh look Carolina's sucking her thumb, it must be time for bed or first thing in the morning or right after nap time or maybe its because the TV is on or it might be because she is thinking or it might be just 1:27pm... I guess you get the idea, she sucks her thumb pretty much all the time. We know its bad for her teeth, but what can you do? I think there are worse things she could be doing. Whats better then hanging out on the coffee table playing your Leapster and watching cartoons?