Don't try this at home (if your home somehow has lava?). But this video shows what happens when you step in lava that's burning anywhere from 700C to 1200C. You don't exactly sink in and become engulfed in the molten burning red liquid, you sink a little bit and then catch fire.
This video shows how pressure applied to this dense material only causes a slight indentation. While this may not be surprising (it is liquid rock), I think that many people think of lava as more of a hot-watery-like substance. You would never fall into a lava lake the way you would a swimming pool, the molten rock is much more dense, so you would simply land on it, sink a little, and be burned.