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At some point, the parents would throw the babies out themselves. This might just be that time.
I would keep an eye out for them but try not to disturb them too much. Try to keep cats and dogs away and see what happens.
Mom and dad should continue to care for the baby left in the nest. The bad thing is that mom and dad can't pick them up and return them to the next like dogs can. If you wash your hands well first with a soap that does not smell, you can pick them up and place them in the nest and mom and dad will be none the wiser.
Let me know if you still have questions.