Hello,
White patches on babies are not unusual.  The cause can depend on a lot of things.  When you look at the patch is it white because it is scaly or white because there is a loss of pigment?  
Most often, it's 
pityriasis alba, a fancy medical term for a white spot!  Most likely on the cheeks, but I've seen them everywhere.  Also, friction can cause an area of whiteness in comparison to other skin.  
Sometimes it's a 
birthmark that has enlarged and become noticeable as the baby grows.  But there are some more concerning 
white spots.  
Much less likely, but possible, is a depigmented white spot called an "ash leaf" spot because it is irregular, mostly oval and shaggy-edged.  
This can be indicative of a very very rare disease called 
Tuberous sclerosis.  This can be related to seizures, so I'm glad you're already scheduled to see a 
Neurologist.  So while you're there, ask them to take a look at the white patch so they can tell you if it is just normal or not.
Hope I have answered your query. Let me know if I can assist you further.
Take care
Regards,
Dr. Lisa Baker