I have long ass hair too, passed my shoulders. Don't make them cut it. Hair is hair and if they like it let them keep it, as long as they wash it and stuff that is good, if they dont wash that shit and it gets all dry and stringy and knotty, then make them cut it.
Main reason parents make kids get there hair cut is because they think they are pot heads with that hair, there 7 and 11, no need to worry about that.