ๅญใฉใใใกใ
Iโm pretty sure ๅญใฉใ is not necessarily plural. In fact, the main meaning on Wanikani is child, not children. Same on Jisho, they differentiate ๅญใฉใ as child/children and ๅญใฉใใใก as children specifically.
ใฎใใจใ
Iโm pretty sure this usage is the one described in this Tofugu article, to talk about someone/something as a whole entity. Relating that to the example Tofugu gives, itโs specifying that the children donโt just like Karen, they like everything about her.