How can I word this request to be as effective as possible?

Where I work, there has recently been a change in upper management. Before, the GM would allow us to bring our children in here and there, and if there was an event, employees' children were always invited. Someone else decided to bring her misbehaving son in DAILY the past couple of weeks, and the new GM has now reneged and decided that children should no longer be allowed. I have a very well-behaved 11-year-old who is CRUSHED by this news. She loved coming to work with me occasionally and had a blast at the events we would hold. She never got into any kind of trouble and is a favorite with other employees and clients as well. I am tempted to have some clients write letters to the new GM demanding that she be allowed but I'm worried it might backfire and I'll get into trouble for discussing it with them in the first place. So I am going to write a letter to him myself, asking him to reconsider in her case. She is not a little kid and does not cause problems for anyone. I want to write it in a way that will not look whiny or nagging, or rude or demanding, or anything like that. I am middle management level and don't want to screw myself out of any potential promotions, etc. But according to one of the newer managers, who has worked with the new GM before, he might be inclined to allow my daughter to come back just on an occasional basis if I write a convincing letter. What should I say??