Can you let your son play a part? If you're doing cake.. Let him help cut it? Or whisper it to him and let him tell everybody, or let him open the box of balloons, you get the drift, whatever your reveal method is, include him. So when you look back, and see pics, it can be 'look what big important thing you got to do on your second bday, what a special day for many reasons'. Vs his bday getting trumped by a big announcement.