If by saying without destroying it, you mean to a keep a reference to the children, you can do:
var oldChildren = [];
while(element.hasChildNodes()) {
oldChildren.push(element.removeChild(element.firstChild));
}
Regarding the original tagging (html css) of your question:
You cannot remove content with CSS. You could only hide it. E.g. you can hide all children of a certain node with:
#someID > * {
display: none;
}
This doesn't work in IE6 though (but you could use #someID *).