Hello,
I believe you have something confused. Unique Constraints are not related to parent/child table relationships.
A Unique Constraint is a rule that values entered for some key must be unique. For example if a key is "country_code" and only one of each "country value" is allowed, this could be enforced by a unique constraint.
I delete all the children tables and there is no problem but not the parent.
I don't know what this means - please clarify.