There are two ways to achieve this achievement, throughout the game you must go through Hunting Grounds
where you will find several of these baby seals
, you can use this place to kill them leaving and entering Hunting Grounds but this is not the best method, the best way is in Norberg Town
there you must enslave some humans where they will be working for you, north of Nordberg there will be some slaves who will make equipment and forge weapons for you, there you can see there will be some of these baby seals
, go to this place with your minions and press
right in the middle to leave your minions on guard, now just let your minions kill them for you.