My heart goes out to Boston. There are a few PC members I know up in that area, so I was relieved to see that they updated that they were fine on Facebook. Thank God. But even still, three lives lost is too many, and I hope all the injured folks make it through as well.
And about the children thing, it's sad that anyone had to die from this, but when children are singled out in these events, you have to understand that that's another child that won't get to grow up and live to see their first kiss, their prom, their graduation, their wedding, etc as well as parents that won't see their child go through that either. And also, children can't do as much to defend themselves like an adult can. So when there's just malicious slaughter of a child, it's just...taking someone that can't do anything to help themselves, really. But even some adults can't defend themselves either, so there's still that. Though it doesn't diminish the other two people that died, but there's just something so particularly despicable about robbing someone of these major, and even little things, in life. But saying that, it also goes for the two other people that died. Not sure of their ages, but I'm sure there are many things they and their families will also miss out on because of this tragedy, and that's not okay.
tl;dr Every life is important, regardless of age, race, sex, etc.
Edit: I just saw a picture of the 8 year old girl that died and just started crying. It's worse when you actually see their face...sigh.