Doctors suspect my kids have congenital myasthenia. i understand what it is, but i want to know if this affects their life span. they have mild cases.

You need expertise: Congenital myasthenia is rare and genetic, and is a lifelong experience with fatiguable weakness. These cases do not respond to immune therapies, and there are at least 4 subtypes that are handled specifically. One variant improves over time. This should not affect lifespan in most cases. You are urged to locate a pediatric neurology department in a prominent medical school to get precise rx.