I'd add that #2 also has a lot of emotional appeal. Kids are having a grand time despite the ramshackle and dangerous environment. The kid on crutches is enjoying himself as much as the other healthier kids and the two kids playing grab-a$$. The other two, 1 and 3, , despite the common public appeal, are meh compared to 2 and 4. Who cares about form, although the hole framing in 4 does add a little interest. But the kids are what make the shot so great.
The contact sheet for #2 shows that he was very keen on that composition of the wall and tried quite a few things out. It's in the Magnum Contact Sheets book.
