Two things:
1. There is an agent within a few feet of Bush in that shot, most likely one on each end of the kids. They are not worried about the kids, they are worried about all the adults that are in the same room.
2. I promise you there are lights on Bush as well, there is always lights on the president. There are people who sole job is to light the president.
In the Obama shot, it appears to be a direct to camera address that happens to be in a classroom. He often does this on visits to schools. I know it would not be beneficial to your point to show any one of the countless times he has sat reading to kids in a school.
To be clear, I am not a Obama supporter or basher. But this sort of bashing is just dishonest. Comparing pictures of two different type of events is like comparing apples and jet fighters.
****EDIT****
Here is a picture from the event at the same school with the kids. The picture posted above was from a media only event at the same school.