if I got you correctly, you have already the parents and the children data and it’s about viewing it, there are multiple implementation options here but the one that could help you easily is to have a list or grid view that will show the parents data and a data view beside it and use the option of the data source to be listen to widget and select the list view and add another list view inside the data view to show the children data.
there are other ways to use non-presistable entity as Helper and to have a flag of show and hide inside the parent List View