How to set focus to the first child element of a specific div?

Hello ;

I have one div Element with id="nav-group" which contains another child element input type='text'

 <div aria-labelledby="nav-group-tab" class="tab-pane fade show active" id="nav-group" role="tabpanel">

I'm wondering how to set focus to that child Input not by Id but by position (First) ?

Thanks