When to treat tectal glioma?

My daughter, 3, has a tectal glioma which is also the cause of her hydrocephalus for which she had a VP shunt placed.

As patients tend to be on the "watch and wait" with regular MRI's, I am interested to know what amount of tumor growth is acceptable (and over what period of time) until it becomes something that requires treatment.  Much of the research I have read says the best course of action is merely to watch it (unless of course it comes to a point that warrants treatment).  I have been told that 10-25% growth or shrikage is considered "stable".  Some have told me that it is expected that these tumors have some growth as the child develops.  What critera must the tectal glimoa meet where it becomes something that can continue to be watched or require treatment?

Thank you, Amy