I have never, never heard of NF having stages and it is not true that the older the patient is at diagnosis the the milder the disease. It certainly does not only affect 2 generations only. These are the true facts. NF is one of the most common diseases affecting 1 of 3000 people. Many perople have NF and are never diagnosed with it because all it caused were chocolate birthmarks.
Some cases run in families but most are new gene mutations.
There is also NF2 but that is not what your discribing. Your child may only get the birthmarks or maybe get other symptoms. There are not that many symptoms as the previous author described. If your child has only the birthmarks what my neurologist recommends and many do, is to have a MRI of the brain and orbits every other year if all is well and see an eye doctor yearly. Also, a neurological examination yearly.