>I tried that but when the form loads, the child combo box using the select statement filled with three records that all had the same foreign key value but I do not know why it filled with the records it did. The parent box brings up all the records in the parent table so when the second combo first loads, how did it decide which primary key field in the parent table to look at?

Maybe the first one? The record pointer has to be somewhere when a table is opened, it was probably the first one in the current order.