Android incorrect behavior of child CheckBox

I have a custom ExpendableListViewAdapter. Like this:

• Group
  • Child
  • Child
  • Child
• Group

All his groups and childs have checkboxes.

I want parent CheckBox to dynamically check itself when all his children are checked.

How to implement this?

I've implemented selection of children then the parent element selected.

This is my method for it:

    void selectGroup(boolean isSelected) {
    for (Item itemChild : item.getItems()) {
        if (isSelected) itemChild.isSelected = true;
        else itemChild.isSelected = false;
        itemChild.setSelected(isSelected);
    }
    notifyDataSetChanged();
}

And I summon it inside getGroupView:

    holder.cbChild.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
            item.isSelected = isChecked;
            item.setSelected(isChecked);
            if (getChildrenCount(groupPosition) != 0) {
                selectGroup(item.isSelected);
            }
        }
    });

And it works fine.

I've tried to implement parent selection as well.

Method:

public boolean isAllChildrenSelected(int groupPosition) {
    int selectedNumber = 0;

    for (int i = 0; i < getChildrenCount(groupPosition); i++) {
        Item itemChild = getChild(groupPosition, i);
        if (itemChild.isSelected) {
            selectedNumber++;
        }
    }

    if (selectedNumber == getChildrenCount(groupPosition)) {
        notifyDataSetChanged();
        return true;
    } else return false;
}

And I summon this method inside my getGroupView as well:

if (getChildrenCount(groupPosition) != 0) {
        if (isAllChildrenSelected(groupPosition)) {
            holder.cbChild.setChecked(true);
    }
}

And then, in getChildView inside setOnCheckedChangeListener for child CheckBox I summon notifyDataSetChanged();.

But I'm getting some strange behavior - for example, if group have 3 childs and I'm trying to select the 1st one, it selects the 2nd and the 3rd.

I think, this is because I putted notifyDataSetChanged(); in a wrong place, but I cannot figure out where exactly and how to fix it.