SPOILERS ahoy...
Great issue (more on that later) except the rational for sending in Nightcrawler to investigate was a bit forced. [spoiler]Storm thinks that either Seth Walker murdered the other kids, or someone teleported in and did the deed?[/spoiler] Sorry, don't buy it.
C'mon, this is the Marvel universe we are talking about! Off the top of my head, I thought of half a dozen other ways[spoiler] the kids could have been killed...
Someone became intangible, slipped into the room, became solid, killed the kids, became intangible again, and slipped back out.
Or...
A time traveller froze the time/space continuum, materialized inside the locked room, killed all the kids, jumped back into his proper place in reality, and unfroze time.
Or...
Some villain used a wonky Kirby-tech device and killed the kids from a distance.
Or...
A telepath took control of the security guard, had him unlock the door, kill the kids, re-lock the room, clean up, and then wiped his memory of it.
Or...
Someone with powers that work at a distance, such as Magneto, used their abilities to kill the kids.
Or...
Someone from the Microverse grew to regular size in the room, killed everyone, and then shrunk back down to Sub-Atomica.
Or...
A sorcerer used spernatural powers to cause a demon to materialize in the room, slaugher the kids, and then disappear back to the netherworld.
See, the possibilities are endless! After all, this is a world where a 100 foot tall alien in purple armor stops by to try and eat the Earth on a semi-regular basis!
By the way, the fact that I am so easily able to come up with so many possible hypothetical ways to kill a bunch of little kids in a fictional setting is a bit unnerving, isn't it?
[/spoler]