Get Child World Position

var config = {
    type: Phaser.AUTO,
    width: 800,
    height: 600,
    backgroundColor: '#010101',
    parent: 'phaser-example',
    scene: {
        preload: preload,
        create: create
    }
};

var game = new Phaser.Game(config);

function preload ()
{
        this.load.setBaseURL('https://cdn.phaserfiles.com/v355');
    this.load.image('lemming', 'assets/sprites/lemming.png');
}

function create ()
{
    var container = this.add.container(0, 300);

    var sprite = this.add.sprite(0, 0, 'lemming');

    var text = this.add.text(10, 10);

    container.add(sprite);

    this.tweens.add({
        targets: container,
        x: 800,
        duration: 3000,
        yoyo: true,
        repeat: -1,
        onUpdate: function ()
        {
            var p = container.localTransform.transformPoint(sprite.x, sprite.y);

            text.setText([
                sprite.x,
                sprite.y,
                p.x,
                p.y
            ]);
        }
    });
}