I didn't pick up DSs from school that day because: 1. Their schools are VERY close to where I live, just about a 3 minute drive, so I know I could be there very quickly if I needed to. 2. Our town is VERY small, so I knew there wouldn't be a big traffic mess if I had to get them quickly. 3. The incidents weren't happening nearby, so I thought rather than scare them further, I'd leave them in school.
I DID call the elementary school to ask if they'd be metioning what happened, to the kids. She said she thought the older grades would discuss in their classrooms.
Of course I watched TV like a hawk that, (as did almost everyone else!) and IF I had seen anything that indicated an attack on Boston (I live only a half hour away from there), I definitely would've gotten my sons and brought them home.
I definitely understand the parents in and near the NYC and D.C. areas who picked their kids up. Or really, ANY parents who felt they needed to pick their kids up and bring them home. It was such an uncertain time for all of us.
I also feel I made the best decision for my own DSs that day. When they both came home from school that afternoon, I asked them what they'd heard already, then took it from there. We let them watch a LITTLE of the news that day, then didn't let them see it at all. We made sure to keep cable channels on while they were around. I believe it would've been hard for them to see it over and over and over, and hear all the speculation that was being discussed at the time.