This is a pretty good start to a story and it is pretty well developed. I am very interested in these new creatures you have created.
Are you planning on fast-forwarding through the coming year or showing it in detail? And how will Harry cope from going from being an adult to being a one and a half year old? And what exactly do you plan to do about Voldemort attacking? These problems could be major plot problems if you let them, but they can be avoided and make the end result all the better if you are a strong author.
These first few chapters are certainly strong. I can't wait to see where you go from here.
Lady Mage