Multiple checkboxes selected in ExpandableListView with OnChildClickListener

I've got an ExpandableListView with my extended ExpandableListAdapter which contains my data (headers = ArrayList; childs = Hashmap).

My custom layout contains a TextView and a CheckBox, which can be toggled by clicking the child.

XML childView

<RelativeLayout xmlns:android="http://ift.tt/nIICcg"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/frag_search_item_layout">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:text="@string/vodka"
    android:id="@+id/frag_search_item"
    android:layout_margin="15dp"
    android:layout_centerVertical="true"
    android:textSize="18sp" />

<CheckBox
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/frag_search_checkbox"
    android:layout_alignParentRight="true"
    android:layout_marginRight="20dp"
    android:gravity="center_vertical|center_horizontal"
    android:layout_centerVertical="true"
    android:focusable="false"/>
</RelativeLayout>

OnChildClickListener:

expListView.setOnChildClickListener(new ExpandableListView.OnChildClickListener() {
            @Override
            public boolean onChildClick(ExpandableListView parent, View v, int groupPosition, int childPosition, long id) {

                CheckBox check = (CheckBox) v.findViewById(R.id.frag_search_checkbox);

                check.setChecked(!check.isChecked());

                return false;
            }
        });

This is working fine but when I select a child, not only its CheckBox is toggled but also a random other CheckBox from another category of the ExpandableListView.

Here is an example: Example

When I click on "Vodka" not only the Vodka-CheckBox is toggled but also the Limettensaft-CheckBox. (Same when I uncheck the CheckBox)

I have not the slightest idea why this is happening but it totally screws up my results, since there are other methods triggered when a CheckBox is checked/unchecked.