Finch Not Sitting on Eggs

We've had a pair of zebra finches for a few weeks. I just discovered 3 eggs in their nest. They had to have been laid in the last 12 hours, as I noticed she was very plump yesterday and now she is not. I am guessing they are still young finches. They are not sitting on the eggs. Is this normal for them?

Thank you!

By fostermomma