Hi Alex,
Thanks for using Syncfusion product.
In order to create the child table for each parent record, you can use the TableDescriptor.Relations property. By default, the GridGroupingControl will create a relation (RelatedMasterDetails) for each DataRelation found in a DataSet. So, you can create the relation in DataSet and bind that DataSet with GridGroupingControl by using DataSource property.
Please refer the below UG link,
Dashboard Sample location: <Install_Location>\Syncfusion\EssentialStudio[Version_Number]\Windows\Grid.Grouping.Windows\Samples\Relation and Hierarchy
Regards,
Mohanraj G