I first wrote a note, but opted to deliver the message in person as they were home [also handed them the note at the end of it as it had my phone number and email on it should they need me]. At the end of the day, i think I've turned what was potentially the beginning of a bad situation into something that brought us closer together and more likely to communicate effectively in the future.
Edit: One thing some people are saying further down is regarding admissions of guilt and i forgot to touch on that but it's clearly what I did here...
I think we live in a society that is often scared that doing the right thing [often in the form of apologizing] will get us in trouble. Plenty of times this holds true, but i think if we all did it more often it might be for the greater good, plus sometimes getting in trouble teaches us a valuable lesson. Doing the right thing should be your priority, but when you mess up I feel it's very important to correct it or you will often suffer small but longer lasting side-effects [stress, bad relationships, etc].