Children position in tween

I have a container, which is used in tween.

this.tween_zone = this.tweens.add({
targets: this.container,
y: gameOptions.GAME_H+this.container.first.displayHeight*this.container.list.length/2,
ease: 'Linear',
duration: 8000,
onComplete: function(){
        				for(var obj of this.targets){
        				this.tween_zone = null;

I need to know if a child has crossed a particular position.

In this example, I need to check if rectangle went below the ball. I will be glad to get help!

Okay, I try this one, but not sure that it is correct

update: function () {
		this.container.iterate(function (obj) {
			if ( === 'Rectangle') {
				if (obj.getBounds().y >= this.ball.y+this.ball.displayHeight) {
		}, this);