When puberty is coming, it helps a lot to have some information about what to expect. Even if you don't want to talk about it directly to your mom, ask her to get you some books on puberty written for pre-teens. There are also websites on the subject written for kids your age and they answer questions very clearly. Look up "wet dreams" if you are a boy and "vaginal secretions" if you are a girl. All kinds of stuff comes out of the body at various times that is normal, don't worry.
By your profile, I'm going to assume you are a male (boy).
First of all, I just wanted to tell you that I would not be afraid to talk to your Mom or Dad about anything that may be going on with your body. At 9 years old you may start experiencing things that you should talk about with somebody you trust. If you are scared to go to your Mom or Dad, can you go to an older brother or sister, Aunt, or an Uncle?
Second of all, I want to assure you that what is happening is perfectly normal, so please, do not freak out about this. Are you having certain dreams when this is happening?
I'm just thinking at 9 years old, you should talk to somebody in person, somebody you can trust.