If you set up a field in the parent table with an auto-enter calclulation that combines the date, track and race number values in a single text field. You can set up a "unique values, validate always" field option on that field and then you can import this data into the parent record and the duplicates will be omitted from the import giving you one new parent record for each unique combination of race, track and date.
To link the child and parent records, I'd use two table occurrences of the parent table in order to set up two relationships.
One would match by Date, track and race and the other by foreign key to primary key. Set up the Foreign Key field to auto-enter or look up the value of the matching parent record's primary key. You then use the primary key to foreign key relationship throughout your database, and only use the other relationship to set up the matching values in the primary to foreign key relationship.