Yunus and Hasan state that a lamb will not be counted and it will not be taken in zakat.

10251 - From Yunus, from al-Hasan (they both said): The kid is counted, but it is not taken in charity.

Hazrat Ibn Jurayj says that I asked Hazrat Ata whether the young kids of goats should also be counted (when collecting Zakat)? He replied, Yes.

Imam Zuhri states that the counting will be done of the young goats at the time when their mother has given birth (to them).

Hazrat Bishr bin Asim narrates from his father that Hazrat Umar assigned his father the duty of collecting zakat in the regions of Ta’if. (His father) counted their goats by including the small kids. The people said to his father: If you are counting this small kid while collecting zakat, then take this small one as zakat as well. He stopped from doing so until he met Hazrat Umar and explained the whole matter to him. He (Hazrat Umar) said: Count the small kids along with their goats when counting, even if (the kid is so small that) the shepherd brings it in his hands, and inform them that indeed for you, the small suckling kid, the pregnant goat, the goat that has been fattened for the purpose of slaughter, and the bull (male animal) that has been set aside (i.e., these will not be taken into account when taking zakat). However, the kid that has not yet completed a year, the eight-month-old kid, and the goat whose two of the front four teeth have appeared, these will be taken. By doing so, there will be justice and equality between the best and the lesser animals.

It is narrated from Hazrat Hasan bin Muslim that the Holy Prophet (peace and blessings be upon him) sent Hazrat Sufyan bin Abdullah to collect Zakat and said to him: Take the animal that is between a very young animal and an old animal (that is, the one of middle age).