1)
Why did he say that it was a small lamb?
1.
Malbim: It hints to Bas Sheva; Chazal 1 say that she was a minor.
1
Kesuvos 9a. Sanhedrin 69b says that she was six years old. (PF)
2)
Why did he say that the Oni bought the lamb?
1.
Radak (1), Malbim: It is a parable for Uriyah, who acquired his wife through Kidushin.
3)
Why did he say that the lamb grew with him and his children?
1.
Radak (1), Malbim: Uriyah had children from a previous wife, who had died.
4)
Why did he say that the lamb ate from his bread?
1.
Malbim: The sin is greater due to his great poverty and the great love he had for the lamb.