I wonder why all ten year old children do not know that numbers up to one hundred should be written as words. Snow White and the 7 Dwarfs does not have quite the same ring as Snow White and the Seven Dwarfs.
We are used to seeing the range: 11+ or 11 Plus or Eleven + or Eleven Plus. If a number is used as a figure it can be written as a number. I suppose we could write 11+ in Roman numerals as XI +. There is a convention that names of Kings, Popes and Emperors have Roman numerals as in Henry VIII. Of course we can also write Henry the Eighth.
We can allow our children to become little emperors for very short periods. An emperor is a ruler. We do not want our children to dictate what and when they are going to learn. They should, however, learn to write some numbers as words.
It does seem better that we think about our children as little princes or princesses. This allows us to remind our children that they have not yet attained the throne. Children do need to work towards winnings the hearts and minds of the people (especially their parents).