Dealing with broken promises

I was reading Lois Melina's book on Open Adoption and there's a chapter on dealing w/ this sort of thing. She suggests using age appropriate discussion w/ the child about it. I think the example's something like a bdad promising to take a child to some ticketed event that he didn't really have any tickets to. Melina suggests talking to the child about why the bdad made the promise to begin with (probably really did want to take the child) and why he didn't keep the promise, what happens when we don't keep promises (people are sad and disappointed) etc. 4 might be young to have that kind of discussion, so I'd agree you want to limit the number of situations where that can occur, but in general, Melina's advice seemed sound too---there are undoubtedly going to be disappointments along the way, so maybe you have to give kiddo some tools to handle it in addition to addressing it w/ bmom.