Get the NIDs in parent-child relation with multiple value fields

Hi,
I have a parent-child node relation based on multiple values, and I need to get the node's ID of children (even if only in a template variable, not necessarily in visualization).

I think I set up relation correctly, but I can't achieve what I want.

The configuration is:

Relations:
- Content: Child.

Fields:
- Node: Title (parent node, then without relation),
- Content: Child Title (link) (node reference),
- (Child) Node: Nid (child node, then with relation),
- Content: Date value (necessary due to bug in Date module I knew from Forum).

Parent node can have multiple children.
The calendar shows all children if I check "Group multiple values" in the node-reference, but shows only one child NID (the first one).
It show only one child node if "Group multiple values" is unchecked, and the showed NID belongs to this one.

I also tried to substitute "calendar" widget with "table" widget and every thing works, both grouping and not; without grouping (that is what I need) I see as many rows as children, with their correct NID.

Do I miss something in the configuration or still it is not possibile to achieve?

Many thanks for Your work.
Best regards.