Equal Opportunity
Let's revisit this concept in a bit more detail (thanks to Greg for raising it). There is no requirement of justice to ensure that all Americans have an equal opportunity to succeed. It's bad luck to have more daunting obstacles to surmount than the average. But it is not unjust that there is such bad luck or that it goes unremedied by others. If it were unjust, then this could be so only because everyone deserves to have as much happiness as his character would allow were there no unusual obstacles to his efforts. But there are two kinds of case that show that this isn't so. First, the case of one child: Abe, who starts out at the bottom: poverty, disease, bad parents, and a bad neighborhood. Abe achieves an unusually good life through the efforts he makes to improve his situation. Having achieved such happiness, Abe has no claim on Americans to provide him with even more happiness. He might have been even happier, had he had an equal opportunity (i.e., an opportunity equal to the average person's). If Americans ought to have given him an equal opportunity during his youth, then since they failed to do this, they owe him even now. But they do not, so they did not.
The second case is that of two children: Amy and Alan. Amy is upper-middle class, healthy, and has good parents. Alan is very rich, has an astonishingly supportive extended family, exquisite schooling, etc. It is not unjust that Amy's opportunity is not as good as Alan's. Nobody owes Amy an equal opportunity to Alan's.
The case of Abe shows that it is not unjust to have an opportunity worse than average, and the case of Amy and Alan shows that it is not unjust to have an opportunity worse than someone else's. Differences in opportunity, like gaps in wealth, are morally irrelevant. There are matters of justice here. First, anyone who wrongly causes another to have a worse opportunity in life than he otherwise would have had has a debt to his victim. People who abused Abe owe him recompense. But other Americans do not, since they did not abuse him. Second, if someone of decent character fails miserably through no fault of his own, consequently ending up destitute and temporarily or permanently unable to provide himself shelter, food, and simple medical care, then other Americans, being quite wealthy, should break his fall with a welfare net, temporarily or permanently, as the case requires. But this is a matter of end-state justice, not initial opportunity. All initial opportunities, no matter how miserable, are just.
On the other hand, as Greg pointed out in comments below, there is a sense in which Americans ought to do something about the poor opportunities some children face. We should do so in cases in which the benefit to the children will be very high, relative to the cost to the rest of us. But this duty is not a matter of equalizing opportunities; it is a matter of improving society and maximizing happiness at little cost, so that its members have better lives. If you see an old man who might have had a good life had he had better opportunity early on, then it is appropriate to wish you could have improved his opportunity. This is a reason to provide vaccinations to poor children, for example. It is a reason to station more police officers in troubled neighborhoods, so that poor children living there will be more secure and better able to play and study. It is also a reason to provide education to poor children, although the benefit to society of having an educated population is already sufficient to make it prudent to do this. In addition, it may be cheaper to improve opportunity now than to pay the welfare bill later. If we can do a few things to help a child now, this might stop him from unfortunately landing in dire circumstances later.
Of course, whether the government or private charities should provide improvements to opportunity depends upon the efficiency we can expect from either. In addition, if we decide to have government provides such services, we should be vigilant about seeing to it that government doesn't interfere with liberty or encourage dependancy. We don't want the government to design people's lives. But government vaccination programs do not do this, nor do police officers. We should be conservative in recognizing problems, considering costs, and assigning remedies.