At some stage stilly the parents have to be responsible for their kids choices...a four year old past the stage of nursing hopefully ( but their lies a whole new thread) can have a boiled sweet or not...their parent knows if they have mastered sucking or not...presumably four year olds who don't know how to suck a sweet have something else supllied by their parents.
The worst kind of child on the plane is the one with parents who are not used to flying...their parents are ill prepared.