Charlotte is moving through our living room

About one or two weeks ago, Charlotte has started to move also forwards through our rooms. You cannot really call these movements (high or "hands-and-knees") crawling but it is de facto low crawling (on her stomach). After today's baby swimming, I have also the impression that she sometimes tries to get her knees on the ground. And she is getting faster and faster each day. We really need to start making our apartment childproof.