$('#check-all-parent').click(function(event) {
if(this.checked) { // check select status
    $('#check-all-child').each(function() { //loop through each checkbox
        this.checked = true;  //select all checkboxes with class "checkbox1"
    });
}else{
    $('#check-all-child').each(function() { //loop through each checkbox
        this.checked = false; //deselect all checkboxes with class "checkbox1"
    });
}
});

<input type="checkbox" id="check-all-parent">hello
<br />
<input type="checkbox" id="check-all-child">hello2