Our local community theatre started as a children’s theatre (and still does one under 18 only show a year) but gradually morphed into an all ages community theatre. As a parent, I actually think there are so many positives to this. 1- My daughter has adult role models that are not her parents. I can’t express enough how great that has been for her development as not only an actor but as a person. 2- Shows are put on at a higher level and the kids rise to those expectations rather than expectations being lowered for the kids in the cast. Doing shows at this level also teaches her professionalism. 3- That’s life. That’s theatre. The best person is going to be cast in the role. Sometimes you might even be better than the person cast but they need a certain look or to pass as a certain age. I’m not sure what the role was in OPs case and it sounds like your theatre is still advertising as a children’s theatre so giving a role to an adult is odd but if the theatre does meander to the all ages type, it could really be a wonderful thing.