Get children in hierarchical content through OOTB web servic

Hi,

I am using OOTB web services exposed by Sitefinity 9. I created a hierarchical module using module builder. For e.g. Foo and Bar, and Bar is child content type of Foo. So if I get an item of Foo type I want get all Bar children from Foo through web service. But i am unable to get that list as there is no such service available as per my understanding.

Let me know what is the proper way to get all the Children of some parent item created using Hierarchical module. 

Please suggest.

Thanks

Chaitanya Gadkari