It could have been Pyloric stenosis only recognised and operated on by a few large hospitals in the 50s. Today it is the second most common operation performed on young babies.
A relation lost a young baby to this in the 50s. The baby projectile vomits and if not treated gets dehydrated and eventually wastes away without anyone knowing what was really wrong. The baby I know of was operated on eventually in Manchester but it was too late. The death certificate says natural causes I've seen it.
Another assassination attempt on Donald Trump


It does sound like SIDS/Cot death. A friend lost her baby that way in the early 80’s. She fed him about 7:30am, put him back down for a sleep and he was gone when she went into his room at about 9:30. 