You can use querySelectorAll:

var childDivs = document.querySelectorAll('#xyz div')

A method to transform the divs to a string (to store or to alert) could be:

var divsHtml = function () {

    var divhtml = [],

        i = -1,

        divs = document.querySelectorAll('#xyz div');

    while (i++ < divs.length) {

        divs[i] && divhtml.push(divs[i].outerHTML);

    }

    return divhtml.join('');

}();

If you need compatibility for older browsers (i.c. IE<8) use @Cerbrus' method to retrieve the divs, or use a shim.

To avoid double listing of (nested) divs, you may want to use

var divsHtml = function () {

    var divhtml = [],

        i = -1,

        divs = document.querySelector('#xyz').childNodes;

    while (i++ < divs.length) {

        divs[i] &&

        /div/i.test(divs[i].tagName) &&

        divhtml.push(divs[i].outerHTML);

        /* ^ this can also be written as:

          if(divs[i] && /div/i.test(divs[i].tagName) {

              divhtml.push(divs[i].outerHTML)

          }

        */

    }

    return divhtml.join('');

}();

[edit 2021] Seven years old, this answer. See this snippet for another approach.