I share your sentiment and I just find it odd that they were at the event. I lost 2 pets in November and I know it is different than children but I am still grieving for my pets and I don’t think that I would have strength to go to a marathon if it was my children but everyone is different I guess.
Like you, I would not be up for any public and strenuous events so soon after a major trauma. Everyone is different - but I put that in as my opinion.
I am also startled that they were so fast. It is noted in the article that they had all already crossed the line before the explosions occured. That means they were in the very front runners of an internationally competetive race.
Running 26 miles at any pace would just about kill an ordinary person. One needs to train. For the Boston marathon, one is competing against the fastest and strongest marathon runners in the world. Lelisa Benti crossed the line as winner at 2.10. Other runners poured in after him, and much of the field still had to finish when then bomb went off at 2.50. The Sandy Hook group, therefore, were within the first 45 minutes. Very fast.