Search within relationships fields from child channel

Hi everyone, I’m building my first EE site and its going great, I’m an EE fan already.

Here’s what i’m trying to achieve: I want the fields (text inputs mostly) inside related entries from another channel to be searchable with the EE Search Form.

I have a parent channel, with some relationships flied where I relate entries from a child channel, all this fields have the “Include in search?” option enabled. But when I try searching a word within a field inside a related entry from the other channel, no results are displayed. The child channel is not included in the search tag (exp:search:simple_form channel=“only_parent”), because I don’t want to search the entries in the child channel, I want to search only the entries in the parent channel that includes the keyword in some field inside the related entry from the child channel.

Hope someone can help me, I expect this to be an easy thing to do with EE.

Thanks in advance!