Implemented child nodes of closing structures calculation. Related to Issue [WTI-550]git-svn-id: https://repos.deltares.nl/repos/WettelijkToetsInstrumentarium/trunk@5733 5a3db67b-de53-47b5-99c8-a1c30a6650e2Former-commit-id: 736aea193e5c4a2d496f5351ec12d33ed8da81b8Former-commit-id: 808153db97a12a548a45ca84d63ee873ab9d9670