I don't really understand if you mean for using C2 or your actual product but I am in the US the most I see people worry about is not using Someone else idea or content, have rights to any music you use. If your targeting children you app can not collect information from them due to the child information protection online privacy thing. Also if it a kids aimed app minors can't agree to contract. But if its your original idea nothing really but setting up a tax id so you can pay US taxes on any US based sales. If you want to be known as a business register as a business in the US for when you file taxes. That is all I can think of right now.