I work mainly with diagrams visible, and the Property Box open on RH side.
For a child who dies before maturity - 'Add fact>Add child count' = 0.
Right-click the diagram, then on 'Diagram options>General' there is a checkbox 'No-offspring marker' and on 'Options' set a vibrant colour for the line.
Now it is instantly obvious in the diagram which individuals will never have descendants.
Also useful for adults where it is known or suspected (none found in GRO) there are no offspring.