Flinch birds

We have a nest in one of my hanging potho plants that had four flinch eggs inside it. Yesterday I saw mom bird and dad bird hanging by the nest around 4pm. Around 8pm I found two baby bird eggs broken on our deck. A third was below in the grass. I never found a fourth. My toddlers were around the nest but usually the momma bird just flies away. She laid her eggs a week ago. As soon as we came in last night, I saw the momma bird and the male bird come back and the mom sat in the nest. I am very confident the mom bird knocked her eggs out of the nest because nothing else could have done it. I just need to know if anyone has heard of this or if it's common? The broken eggs showed a developing bird in each one. I'm just confused why she did that! And where the fourth egg went. If she felt threatened and that's why she knocked the eggs out, why would she bother coming back to the nest as soon as we came inside?