Don't change it higher than 4. It will let you adopt the fifth 'child' but once they come of age (or if the adoption is of an adult), the trait triggers will cause an Unspecified Crash whenever they increment one of the fifth childs traits/stats.

The incrementing part is the key, just having a fifth does nothing until one of the traits increase.

I am using an unmodified export descr character trait file.

Brandon