A kind of relationship in which we can say anything to each other would be ideal.
"A kind of relationship"＝「ある関係の種類」
"in which we can say anything to each other"＝「お互いに何でも言えるような」
"would be ideal"＝「は利用的だね」
A sentence in context:
"It would be ideal, but also difficult, to have a parent-child relationship in which one can honestly say both negative and positive things to each other."
アメリカ合衆国 
