Someone said to me the other day (when talking about a ten year old boy), "He seems fine. You can't tell that his mother died two months ago." I thought to myself that there is no way that that young boy is just fine!
Dr. Alan Wolfeldt always said that "mourning is the outward sign of a loss and grieving is the inner sign of loss." A person may not show their experience with death, but they are still grieving just the same. And sometimes a dramatic, radical change in a person/child's life may delay the outward signs of grieving, but the emotions are still there---just percolating inside.
As with so many others, we found that while the rest of the world goes back to normal our lives were forever changed. We had to tiptoe back to doing some of life's daily business---like taking out the trash, doing laundry, grocery shopping. And I suppose that to those who passed us in the grocery aisle, we may have looked "normal".
We also learned from Dr. Wolfeldt that in bygone days, families used to wear a black armband to show to the world that they were in mourning. This was a visible, recognizable sign that someone is mourning/grieving. People that they encountered had an opportunity to express sympathy and condolences.
What is most important for those who are grieving is the support and compassion that can be shown and demonstrated to the grievers. Whether done on a one-on-one basis or through a support group, that is the best way that I know of to crawl out of the black hole that is experienced with a traumatic death.
But the biggest take-away is that while people who have experienced a death of a loved one may seem fine, they can't help but be hurting from that death. Give them the benefit of your compassion.