For a Multiple Award IDV, child_awards returns the task orders or delivery
orders placed against it. For a parent IDV, child_idvs returns the
downstream IDV structure. grandchild_awards walks the hierarchy.

Field name differences from search_awards: children use 'piid' (not
'Award ID'), 'obligated_amount' (not 'Award Amount'), and
'generated_unique_award_id' (not 'generated_internal_id').

An active vehicle can legitimately return zero children here:
USASpending's award cross-linking has gaps. Treat an empty result as a
reporting gap, not proof that no orders exist. Try get_idv_activity()
on the same id. A search_awards call with keywords=['<IDV PIID>'] only
finds orders whose description happens to cite the IDV, so it misses
orders (often the largest) and is no proof of completeness.