'imho, as they are very healthy children (BFed extended, decent diet, as much as is possible with autism, etc) i'm not worried at all.'
See, this is a point of confusion to me.
In the not too distant past, the vast majority of babies were BFd, often extended, due to lack of availability of formula/expense and contraceptive properties of it.
Many had a diet considered very healthy by today's standards due to no processed foods available and not too much meat due to expense.
Yet they still caught childhood diseases and died.
My dad was BFd for 2 years, just like all his siblings.
They all still caught measles, mumps, rubella, scarlet fever, etc.
His mother has also been BFd in that fashion. She got diphtheria, MMR, etc.
They had an excellent diet - couldn't afford sweets so mostly had fruit, plenty of fresh veg and fruit grown in their own garden, meat only one a week but loads of pulses, etc.