When working with composite records, one input must be set up which contains the main objects (parents) and a separate input must be set up which contains the related composite objects (children). The order of the parent records and the children records is used to match children to parents. As each parent record is processed from one input, the associated children records are processed from the other input.
To mark the end of children associated with a parent, a blank row (all NULLs) much be present in the input. The processing of a parent record is only completed when a blank row is encountered at the end of the children for that parent. The final record in the children input must be a blank row in order to complete the processing. You can use Query transform to prepare child data with the proper blank rows.
For additional information about modelling of composite records in SSIS+, please refer to this article.