inheritance problems

I have a parent with two columns, the primary key; several children 
inherit these columns.

I can see all the childrens primary keys in the parent. however I can't 
reference data in the parent table that was entered into a child. I get 
a referential integrity violation. why is this? is there any way to 
change this behaviour. the purpose of haveing the parent was so that I 
could see the rows of two table in one place so that another table could 
indirectly reference the two of them. but this doesn't seem to behave 
the way it apears it should.

Thank you very much for considering my problem, any help would be 
greatly apreciated