Once he found out what that blockbuster did....

....that should have been his number one priortity.
Even when he does eventually try to fix that incident, it's from the point of view of the psychological damage it does to Lenny rather than the fact that it killed 2 people, including a baby.
Despite the many, many plot holes of this movie, that's the biggest thing that bugged me when i watched it all the way through for only the 2nd time.
While I'm at it, did none of the grown ups, especially lenny's mother, not put two and two together?! Their children suddenly act withdrawn, in Lenny's case flat out traumatised, and it starts the same afternoon that the explosion happens close to where they live??
Actually evan's mum seems to, but rather than ask the other children about it and try to get to the bottom of what happened and that the appropriate person was punished, her reaction instead was to say nothing and move away.
Hard to sympathise with any of the characters after that. In whatever timetime