Maybe it is somewhere in the text and I've missed it, but I'm wondering how Aaron, his brother, avoided death?
I have always assumed that Aaron was born before this decree was made. (He's three years older.) The text only tells us that Pharaoh made the decree and Moses was born (and his mother hid him etc). If Aaron had been born under the decree then I would expect the text to be different from what it is, but we are left to reason from the absence of information -- always a tricky proposition.
You may be being tripped up by 2:1 "and a man of Levi took a wife" etc, thinking that that must precede the birth of all three children. A plain reading would be that what is translated "took" means "had taken" (sometime before); Biblical Hebrew doesn't distinguish clearly among past-tense forms like English does.
There is also a rabbinic interpretation (Sh'mot Rabbah 1:13) that Amram had divorced his wife after the decree and Miriam convinced him to remarry, arguing that Pharaoh condemned all the males but he was condemning both males and females (by refusing to produce them). That interpretation is anchored in this passage.