How to add animation in moment when I change which View/LinealLayout is visible in same activity

Question

I have in RelativeLayout 2 content (only one is visible at the time ) and menu at the bottom which chose what is visible ( and it works, in activity I change visibility to View.VISIBLE/View.GONE

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal"
    android:gravity="center_horizontal"
    android:orientation="vertical" >

    <include
        android:id="@+id/children"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_weight="1"
        layout="@layout/activity_children"/>

    <include
        android:id="@+id/parents"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_weight="1"
        layout="@layout/activity_parents"
        android:visibility="gone" />

    <com.touchmenotapps.widget.radialmenu.semicircularmenu.SemiCircularRadialMenu
        android:id="@+id/radial_menu"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:padding="0dp" />

</RelativeLayout>

How to add animation in moment when I change ( I have animations like fade_in and fade_out)

This is piece of code where I change which content is visible

        llChildren.setVisibility(View.GONE);
        llParents.setVisibility(View.VISIBLE);