Rolling over signs

Hello all. I think my 12 week old is showing the first signs of wanting to roll over but I'm not too sure. Recently when they're on their back. Their body from the neck down has started to twist to the side. There are times when it looks like they might actually roll over but their head is still too heavy and not quite strong enough to move with their body. But is this just general body movement development they're exhibiting? Or if it is the first signs, are there any good exercises to do with them? Thankyou x