I suggest to you to use my favourite function:

 function getQueryString() {

                var queryStringKeyValue = window.parent.location.search.replace('?', '').split('&');

                var qsJsonObject = {};

                if (queryStringKeyValue != '') {

                    for (i = 0; i < queryStringKeyValue.length; i++) {

                        qsJsonObject[queryStringKeyValue[i].split('=')[0]] = queryStringKeyValue[i].split('=')[1];

                    }

                }

                return qsJsonObject;

            }

Just call it from the child window like this and act with the query string as an object.

For example if you have the query string ?name=stack and you want to get it, try:

getQueryString().name

This will return stack.