From when are the seven days counted?
Radak (20): From the birth. 1 Malbim citing Mahari - this is why David did not mourn the child (refer to 12:20:1:2).
Metzudas David: From the illness. 2
Radak: This can even be like Mo'ed Katan (15b), which says that David observed Aveilus due to the baby. Normally, a baby that dies within 30 days of birth is a Safek Nefel. Here was different, for David knew that the months of pregnancy were complete (he had Bi'ah with her only once before Uriyah died).
Radak: It is difficult to say that David fasted and lied on the floor for seven days. (The Rambam (Hilchos Shevu'os 5:20) says that it is impossible to live seven days without eating. Surely there is mortal danger even before this! - PF)
What evil did they fear that David will do?
Radak: He will harm his own body.
Why is this not listed in Bereishis Rabah 92:7 among the 10 Kal v'Chomerim in Tanach (when the baby lived, he did not heed us
Moshav Zekenim (Bereishis 44:8): In the end, the Kal v'Chomer is rejected. (After the baby died, there was no reason to fast.)
