I have mostly seen So jisub in dark roles , This one still being dark can make you laugh , without even saying anything ! Thats the power of so jisub !
Jisub plays a handsome NIS agent/babysitter and he plays them both with utmost conviction ! he will just make u laugh with the way he turns his head ! His time with the kids is thoroughly enjoyable ! The KIS mommy squad is super entertaining .
Actually KIS seems better than NIS :D ... Plot holes definitely exist , but then its fine !

The only thing that annoyed me was the FL character . She was too nosy ... the writers could have given her some good reason to barge into , then probably people would not have hated her ! By this i am not commenting on her acting skills , she was exemplary with the part she was given ! but no one would want an FL who annoys u to this extent ! ;) and then suddenly she became very understanding ! This would be the only flaw I will report wrt this series .

Happy Watching !