The contribution of the ancient Romans to mathematics was limited to some notions of surveying, arising from the need to measure and fix the borders or limits of the empire. However, in Europe, during the Middle Ages, this numbering system was still used. That is why the use of Roman numerals is still observed in our days, in many cases like the numbering of the chapters of a book, to indicate the succession of kings and popes, in the notation of the centuries or to mark the hours in some watches.

Source

It is important to teach the child this type of numbering for general knowledge and the use of it in specific situations.
The first thing is to identify the symbols to facilitate their understanding, the ancient Romans invented this numbering system based on symbols that had the shape of letters. The symbols used by Roman numerals are seven:

I = 1

V = 5

X = 10

L = 50

C = 100

D = 500

M = 1000

However, when we get a horizontal line placed on top of a letter, multiply the value of that letter by a thousand, two lines above any symbol indicate as many millions as units have the symbol; that is, four stripes, as many trillions as units, indicate the symbol; six dashes, as many trillions as units have the symbol. For example:
_
V = 5 thousand

Reading Roman numerals

To read a Roman numeral correctly, the following rules must be taken into account:

• Letters are written from left to right starting with the highest value:
  

  XV (10 + 5) = 15 VI (5 + 1) = 6

• If to the right of one figure we put another equal or smaller, the value of the first is increased with the second:
  

  VI equals V + I = 6

• If to the left of one figure we put another minus, the value of the minor is subtracted from the larger one.
  

  IV equals V - I = 4

• The letters I, X, C, and M can be repeated up to three times second. When we represent 4, 9, 40, 90, 400 and 900, we must make combinations of letters:
  

  XC= 90
  XL= 40
  XX = 20

• The letters V, L and D can not be repeated, since we have specific letters for this:
  

  X (10) = 2 times V
  C (100) = 2 times L
  M (1000) = 2 times D

Fun activities to teach a child to read Roman Numerals.

• Adding and subtracting

Initially, you start reading and memorize the first ten numbers.
I = 1
I + I = II = 2
I + I + I = III = 3
IV = 4 (number five with the one in the front as if it were subtracting)
V = 5
V + I = VI = 6
V + I + I = VII = 7
V + I + I + I = VIII = 8
IX = 9 (which is equal to 10 -1, because the one is before the letter x represents 10)
X = 10

• Memorizing dates

As children like the game of memorizing, it is a strategy to ask for a birthday of their mother or father, for example, May 12th = XII (day) - V (month five) and in this way to propose exercises that are fun and you can evaluate the given learning.

• Play to find an equal partner

With this fun memory game, children's learning becomes more solid and they acquire better knowledge. For this type of activity, it is necessary that you make small pictures on cards with natural numbers and another box with its equivalent in Roman numerals. And all the cards face up on the table so that the child identifies and pairs both cards.

Likewise, with these same cards, if you place them face down, it will become a memory game, where each child takes turns, flips the card and then looks for another card to find its equivalence and thus form pairs.

With a single material two games originated, which would facilitate the speed of understanding this class and mental agility with the knowledge of Roman numerals.

• Building Roman Numbers

In this activity, it is important that children already know the Roman numerals, because only then can they make their own figures. For this game, it is necessary to have sticks of ice cream, glue, and tempera with your brush to paint them.

The teacher will provide the material on the table and write on the board with several simple numbers. Here the child will choose a number from the list and proceed to create it with the wooden sticks and then paint and decorate them.