Obamafoodorama has posts on the actual planting of the White House Garden. Apparently they're planting cool weather vegetables, mostly starts instead of seeds. If they were sowing seeds I'd call them a tad late, since they're in a warmer area than we are. But starts makes sense: that way you can see where your untrained helpers are planting; wouldn't want to have any irregular rows, or rows which drift to the right in the garden. Planted potatoes for the first time which makes sense in terms of productivity.
I observe Mrs. Obama favored girls, particularly Girl Scouts, in selecting her volunteers. I also observe the idea that the Obama kids will garden has faded away. It was a nice idea but this is a show piece with lots of different people with their fingers in the soil, which doesn't make for a good learning experience for the kids.