Zheka
You're right you can't bring him back, but you can keep his memory alive for his failmy. My HUGE suggestion is to write a note to each of the kids & his wife and tell them each a funny or sweet story or anecdote that will make them smile and be proud that their dad/husband brought light to some one else's little world. They will love and cherish that because its something that they may not have known about him and have been able to share with each other, but you can bring the confidence that they love a man who was loved by others as well.