Even though the children who will be blown up don't yet exist, this is still a bad thing to do, because it robs those kids of their future happiness and experience.

Well, it's definitely a bad thing to do because it kills the children. I dunno if I'd follow that next inference ;-).

If you subscribe to the block model of the universe, then time is just another dimension,

Luckily, I don't. It works well for general relativity at the large scale, but doesn't yet some to integrate well with the smallest scales of possible causality at the quantum level. I think that a model which ontically elides the distinction between past, present, and future as "merely epistemic" is quite possibly mistaken and requires additional justification.

I realize this makes me a naive realist about time, but on the other hand, I just don't see which predictions a "block model" actually makes about causality that account for both the success of general relativity and my very real ability to make interventions such as bombing or not bombing (personally, I'd prefer not bombing, there's too many damn bombs lately) a day-care. You might say "you've already made the choice and carried out the bombing in the future", but then you have to explain what the fundamental physical units of information are and how they integrate with relativity to form time as we know it in such a way that there can be no counterfactuals, even if only from some privileged informational reference frame.

In fact, the lack of privileged reference frames seems like an immediate issue: how can there be a "god's eye view" where complete information about past, present, and future exist together without violating relativity by privileging some reference frame? Relativity seems configured to allow loosely-coupled causal systems to "run themselves", so to speak, in parallel, without some universal simulator needing a global clock, so that synchronization only happens at the speed-of-light causality-propagation rate.