Hi,
I’m sorry this happened, but it’s not uncommon. It’s best to leave it all alone. It’s actually against the law to do anything to the nest in the US – wild birds and their nests and feathers are protected by Federal & State laws. If the parents abandoned the chicks, something may have happened to one or both of them. They may have felt the nest wasn’t safe from predators or people and abandoned it. Or something may have been wrong with the chicks. The parents might come back and toss the dead chicks out and nest again. If they never come back, put the nest and contents under a bush or something, to let it go back to nature. Wait at least a week before taking any action.
When you do observe something like an active nest, always keep your distance and try not to disturb the parents. I know this can be hard when they build so close to people, but ironically, having too much human or pet activity near the nest can make them change their minds and leave, even with live chicks in the nest.
Thank you for caring,
Brenda