I agree. If there is a cure then everyone should get it, and in reality, if you are an adult, you are far nearer to complications than a child and should receive it first. That would significantly reduce the overall costs to the NHS.
Also, most new treatments/cures are approved for adults and then only later approved for use in children. So any cure that's at all medical would most likely be given to adults first.
(By 'at all medical' I mean not something you could do yourself. I say this because when I was first diagnosed I had a frequent daydream that the cure for diabetes would be something as simple as not eating X, Y or Z ! )