Congrats Nishy! Being an uncle is the best you can get! You get to spoil them, and have them around while they think you are the best there is, and when they get tired and annoying, they go back to their parents. You only get the good, and very little of the bad
Around them, be you, be the child that's in you, and treat them like a person. They'll love you forever, and best: you them!