Possibly a snake. That happened here and we found the bugger still in the birdhouse, complete with little birdie bumps.
I'm sorry. I know it is the circle of life and all that, but it sure made me sad when it happened.

Oh No!!!!
The poor babies. I had to laugh at the pic you posted and put it as my wallpaper. This breaks my heart.

I'm wondering if it was a bigger bird. I know that the ravens or hawks or whatever will sit outside a nest and squawk. When the babies poke their heads up to get fed, supposedly, the scavenger takes them.

Could it have been a raccoon? We never ever see them during the day but we have tons around here and cause their trouble at night. We've trapped and relocated several. They're very good climbers and have ruined many bird nests. I'm so sorry to read about your baby robins; it's heartbreaking.

Oh, that's terrible!

Oh that's so sad. I'm sorry.

I'm betting a raccoon,too. I had one shimmy all the way up a 20' pole to get to my large bird house, his muddy little paw prints gave him away. How he managed it, I don't know.

Robins build unstable nest many times. It could be it just fell and something on the ground got them. It is amazing any survive after some of the nests we see.

Thanks, everyone. I like the fact that those tiny robins touched many of us in their very brief lives.

The nest appears to be quite sturdy, I'd say. Heavy for its size, and even after falling that distance, completely intact. Robins have been nesting in that spot for years. Do they make a new nest every time? If so, I wonder what they do with the old ones.

I agree with Gardenspice, a snake. We had a bird nest in the shrubs very close to the house, it had several eggs in it. I started out of the house one morning and noticed a snake in the shrub and it had eaten all the eggs. How did that snake know the eggs were there????

Could a snake climb a post? I guess they can do all sorts of things. I looked for a picture of where the nest was situated, and all I could find was this one, photographed from the back of the ice house. My carport is to the right of the ice house, and the nest was on top of the front post, under the roof. In this picture it would be the first post on the left.

There are no tall shrubs nearby, so whatever did it would have to climb the stone wall (about four feet) and then climb the post.

We do have snakes around here, of course, although I haven't noticed any large ones. And I've seen raccoons in the past.

Cat?

It could have been a snake, raccoon, rat, squirrel, cat, skunk...

It could have easily been a snake; they can even climb smooth metal poles, but they don't normally knock down the nests. I'm going to guess it was one of the furry preditors.

Birds are rather low on the food chain, and robins tend to have their nests, and noisy chicks, so exposed.

I'm so sorry you lost your little guys. I hope she nests again.

My robin, Bad Luck Bessie, lost three nests of eggs this year. First to the squirrels, then to grackles, and then to the wrens.

She is now living the single life. Eating and playing in the sprinkler. I don't think she'll nest again until next year.

Your barn is beautiful!

Do you mice/rats also will eat eggs/babies.

I heard on tv last week that alot of the baby birds never make it.We had a nest of cardinals,I saw a mockingbird attack the mother,he threw babies on ground they all died ,IDidnt know he rooted babies and nest to the ground, hes now in a nest in the same bush,
Ive seen him tormented robins in the yard,they bite my dogs in butts when theyre out.
I also saw a starling go up to birdhouse and rip the nest out of the hole.