We are going through this phase with my DS who has just turned 2.

We are teaching him even now that every action has a consequence, even when it comes to choices with regards to food or playing outside or in, shoes or no shoes etc. It is a natural thing for a child to go through this process of changing their mind all the time. We offer a choice and recheck a few times but once his decision is made then that is final. That is his choice. So if DS chooses Vitabrits over porridge then it's Vitabrits. If a tantrum ensues we just let it unfold in front of us but if he needs a cuddle, he gets a cuddle as we never refuse kisses or cuddles in our house. I'm expecting, from what I've heard from friends that this phase lasts for quite a while too