Your question seem not be very clear, but if i can guess what you want to achieve is something of this snippet
var parentElements = document.getElementsByClassName('parent');
for (var i = 0; i < parentElements.length; i++) {
//for each one
var childElement = parentElements[i];
//also you can get the class or other attrb
var childEleClass = childElement.getElementsByClassName('btn- floating')[0];
// perform so stuff with it also
childEleClass.onclick ......
}
solved Java script click event – how to find the child element