Use scissors to make 16 marble-sized holes in the cardboard sheet. Make holes every 5cm, with 4 holes per row. You'll need two identical sheets like this.

Using marker pens, label the holes with numbers in sequence (you can adjust the numbers based on your child's current ability level, for example, for 3-year-olds we can...)

Take the cardboard box and apply hot glue along one of the wide edges.

Attach the numbered cardboard sheet to the glued edge of the box, wait patiently for the glue to cool. Attach the second sheet to the opposite edge in the same way.

Use hot glue to secure the top of both cardboard sheets together.

Glue another piece of cardboard at the bottom of the joined sheets as shown.

Cut card paper into 4cm x 6cm rectangles - you'll need 32 identical pieces. Use marker pens to write numbers on the cards, making two sets numbered 1-16.

Note: For children aged 3 or younger, writing simple numbers is recommended. For children who can do basic arithmetic, you can create appropriate problems based on their ability level - for example, you could write "5" or "1+4=?" to practice mathematical skills.

Now, place some marbles into your chosen numbered holes. Remember, don't let your opponent see where you put them!

Game rules: Players guess which numbers their opponent has placed marbles in. Use rock-paper-scissors to decide who goes first. The first player shows a number card - if there's a marble in the corresponding hole on your board, you must remove it. Take turns showing number cards. The first person to remove all their opponent's marbles wins.