Force Child Realtionship(ZZ23REEWRel) when creating Parent(BuilRealtionship)

Hi,

I have requirement that whenever user creates Builrelationship , they must also fill in child ( ZZ23REEWRel). I tried to achieve this through front end , I was able to show error prevent user going back. But I notice even though I displayed error parent entity ( Builrelationship ) ia already created with out child(ZZ23REEWRel) and allowing to save. Please show some light how to achieve this.

Thanks,

Senthil