Original: Their first-born son died as an infant in 1936, their second son, John (born in 1939) contracted polio, and their daughter, Shirley, born in 1941, had cerebral palsy since her birth.
Simplified: Their second child (John, born in 1939) had a health problem called polio and their third child (Shirley, born in 1941) had cerebral palsy since birth.