I am 17 years old and have been umpiring kids between the ages of 8 and 13 since I was 14 or 15 years old. I have found umpiring to be a very helpful experience in my playing career. I have found that my teammates now come to me to ask about rules because they know I have to know them because I'm an umpire and I can take full advantage of interference/obstruction situations because I see them as they occur while most players do not recognize these situations. As far as dealing with coaches and/or parents my advice would be ignore the parents unless it gets WAY out of hand. Most coaches will not be a problem if you seem confident in your calls. Make them loudly and clearly and be prepared to explain them to the coaches but do so in a calm manner and they will usually respond in one.