What may not be clear to those parents who flatly refuse to move is, if they do not act reasonably it may impact on their ability to use buses at all. Not all wheelchair users can travel by bus. If their wheelchair is too big or heavy they are barred from traveling.
The spaces on buses wouldn't be there if disabled campaigners hadn't fought for them to be there in the 1980s and 1990s. But today many wheelchair users still face difficulties accessing the spaces, often causing a great deal of distress.