What should I do about this robin's nest?

A pair of robins built a nest in a small tree near our front door. The eggs hatched several days ago, but the babies are still pretty helpless. Their eyes just opened yesterday, and they don’t have a lot of feathers. This afternoon, I happened to look over at their tree on my way into the house, and saw one of the baby birds flopping around on the ground. I carefully returned him to the nest, but noticed that the nest is rather lopsided.

For the rest of the evening, we kept a close eye on the baby birds (from a respectable distance, to avoid stressing the adults), and later saw that another baby had fallen out! Luckily, the nest is not very high, maybe 5.5 feet up. I sat on the front steps for a while, and saw that whenever Mom or Dad flies up to feed the babies, they freak out and flounder around in the nest with their necks stretched out. The babies on the side of the nest that has dipped lower are clearly in danger of falling out again.

Should we try to somehow straighten the nest out, or just leave it alone? I know the robins won’t “smell” us on the nest and abandon it, but I also don’t want to make the situation worse. Is there a safe way to stabilize a tipping nest? Have you ever attempted to fix a nest and had things turn out well?