Empty magpie nest

I had a pair of magpies build a nest in a tree just outside my spare room window. They had 3 fledglings that I watched being fed and cared for by the parents over the last couple of weeks, but I haven't seen them in a couple of days or heard them. Do they get easily scared away from the nests even when there are babies?

I had a look on the ground and don't see any evidence that they died or were killed.