Terrible couple of weeks!!!

I have had chickens for over 2 years with no problems at all. Last month, one of 6 shipped chicks died the day after we got them. The worst part? It was the one my 7-year-old son picked out as his as soon as we opened the box. Last week, I got 3 chicks for a broody, and they died one day at a time--my son was devastated. Tonight one of my hens wasn't in the coop, so my husband and I got out the flashlights and went hunting. Found her, dead, under the coop. Whose hen is it? Of course, it is the one my son picked out when we got them 2 years ago. He won't take this well. Now I'm afraid those last 3 chicks who died have brought some sickness to my flock. I'll just have to wait and see, but I'm totally bummed out tonight. I'm sorry about the loss of the chickens, but mostly I feel awful about how upset my son has been, and that it will get even worse for him tomorrow. I'm really not looking forward to breaking the news.