Tonight as I was getting my 3 year old daughter to sleep, I said "today, you took good care of your animals and dolls. You gave each of them at least one toy to play with. The bunny had a teddy, the teddy had some cars, the cat had some trains, and the dog had some trains, too." She perked up and said, "yes, I love them all and take care of them!"
I tell her how thoughtful she is to think of everyone, and she wriggles with happiness, and then drifts off to sleep.
For my 5 year old son, it is the same strategy, but I also think through his day about assertions he had made, and things he has said that I can agree with, and I repeat them to him. It's a longer process, but he, being older, has more to work out before he can settle to sleep. I will tell him that when he was playing outside he did do some amazing circus-type tricks as "Tyler the Magnificent," and I recount what they were (swinging on the 'trapeeze,' running up the slide, etc). For him it also helps to say a prayer and incorporate whatever may be troubling him. We give his worries away.
For both kids, it used to be enough to just repeat "I love you," but this is a new way, a way that says, "I see who you are and what you do, and I love you."