For the kids, I just let the parents take the lead. If they want to bring something for the team at the end of practice I support it, we sing and have treats. If they don't bring treats (almost everyone does), we'll usually just wish them happy birthday. I don't give them anything. I've thought about giving cards or giving trampoline time to the birthday girl, but then I have the trouble of figuring out if I institute it at the beginning of the calendar year or the beginning of the school year to avoid hurt feelings from those whose birthdays have already passed and end up not doing anything.
For my assistant coach, I usually have the kids sign a card and I'll bring cookies for the end of practice. No gifts, most of the kids don't even know ahead of time, but just a little something to show the coach he/she is appreciated.
For me, I don't tell anyone. I hate being the center of attention and avoid it if at all possible. This year (thanks to Facebook) I did have a few kids bring cards and one brought brownies for the team- actually I think they were just supposed to be for just me but HC felt like a jerk that she missed my birthday and took them from the parent and gave to the girls after they sang for me haha.