It's called desire. For an example, when I was a kid, we played baseball everyday (So do they), we played in the street, we played at the park...if we had a brick wall we threw against it....so do they...you on the other hand have a very structured existance, get to play on a nice ballfield...in LL about twice a week with a little practice here and there, travel ball you get more but not much more (If you have little apparent skill you get 2 innings and an at bat..not much chance to develop there)..they do it every single moment and chance they get. They also have few if any ways to get out of the situation they are in, it's much easier to motivate when you don't know where your next meal is coming from or if you'll have a roof over your head...you on the other hand (Typical kids) have so much to distract and make life easier...that is why we have a huge problem with childhood obesity and diabetes. Half the time (Actually most of the time in some instances) you can't get the play station controller out of a kids hand long enough to even spend a little extra time working on our art.
If you would like I'd be happy to forward you Sammy Sosa's biography so you can get some understanding on the subject.
Just pm me with your address and I'll try to ship it out to you when I can. I only ask that you pass it on to another interested kid when you finish and don't waste the book...if you can't find another interested kid, at least donate it to a local library.