Few things in life are more devastating for a parent than losing a child. Your heart aches for your friend, but you might not be sure how to most effectively comfort him. He's understandably going through a flood of painful emotions, and you want to tread carefully when it comes to offering your condolences and expressing your sympathies. Perhaps you feel that never has it seemed more difficult for you to find just the right things to say. There are things that you can both do and say, however, that will offer comfort to the bereaving friend.
Offer your condolences and deepest sympathies, and let her know that you are there for anything she needs. However, leave it at that for the time being. Don't assume that you know what she needs or how she feels, unless, of course, you've dealt with the death of a child yourself. Remember, every situation is different. Sometimes just listening is invaluable for the friend.
Send a card expressing your sorrow about his loss, even if you already have done so in person. At the least, it's a nice gesture that reaffirms that you care and wish to offer comfort. Don't stress too much about writing a long, drawn-out message in the card; short and heartfelt sympathy works just fine.
Share stories of the good times with the child with the parent. Take your cues from him, however, because he might not always deem it a good time to do so, depending on his mood. But positive stories about the child that bring about smiles are a good thing to focus on instead of dwelling on the "what if's."
Give the parent a gift. Use your good judgment as to what is appropriate, because it depends on the grieving friend and how she's handling the loss. A simple flower arrangement at the funeral and a donation to a charity in the child's name are examples of meaningful, tasteful gifts that offer the parent comfort.