Q:

Column 'id' in where clause is ambiguous for 3 tables Codeigniter

I am currently doing a system. In the system, there's a module called manage resident; where the manage resident will get the information of the resident if it is single, married and have a child(first,middle and last name for example).
I've done the adding or create new resident part, I am now in edit resident part. When I click the edit resident, I encountered error 

Column 'id' in where clause is ambiguous

I have 3 tables: resident, married and children. Resident ID is the foreign key of married, while Married ID is the foreign key of children table.
My data example for each table(column Primary key, foreign key, first_name, middle_name, last_name 
Resident -> id, Testing, Testing, Testing
Married  -> Married_id, resident_id, Testing, Testing, Testing
Children -> id, married_id, Testing, Testing, Testing

Question: How can I get the children of the selected Resident? Then display it separately in my fields in my view.
Controller
 $id = $this->uri->segment(4);
 $get_children = $this->Crud_model->get_children($id);

Model
public function get_children($id){
        $this->db->select('*');    
        $this->db->from('resident');
        $this->db->where('id',$id);
        $this->db->join('married', 'resident.id = married.resident_id');
        $this->db->join('children', 'resident.id = children.married_id');
        $query = $this->db->get();
        return $query->row();
    }

View
 <?php $explode = explode(",",$children->first_name); ?>

<div class="form-group">
  <label>First Name</label>
  <input type="text" class="form-control" name="child_fname" id="child_fname"><?= $explode?>
</div>

A:

Whenever you join tables with where condition you should write each column with its reference table name.
so change 
$this->db->where('id',$id);

to
$this->db->where('resident.id',$id);

