Useful code to parse out SSPID and A9 etc from the field schema xml and the taxonomyclientservice xml returned.
Then I checked wsdl of the TaxonomyClientService.asmx (added ?wsdl to the web service url) – and it didn’t contain the definition of the GetChildTermsInTerm and GetChildTermsInTermSet methods. So that was the problem.
As you probably know in Sharepoint wsd land disco files are located near asmx file in format *wsdl.aspx and *disco.aspx. So I checked TaxonomyClientServicewsdl.aspx – and, as I expected, definitions of GetChildTermsInTerm and GetChildTermsInTermSet methods were missing here. For me this looks like a bug.
To generate the WSDL http://sp2010dev.sp2010.local/_layouts/test/taxonomyclientservice.asmx?WSDL