Insert values in child table

You're talking about JDBC + SQL? If so, for most databases you can use (Prepared)Statement#getGeneratedKeys(). For certain databases, like PostgreSQL and Oracle, you have to write a specific query to retrieve the current sequence.

You have to define the column as auto_increment in the DDL. Then, after the Insert query, you can use getGeneratedKeys() of the same Statement or PreparedStatement to retrieve the last insert ID.