Why do this problem?
will help young learners to come to some understanding of factors and multiples leading to a first introduction to the idea of prime numbers. They will need to look at multiples of $2$, $3$ and $5$ up to $20$. For some children just making the table to use will be a useful exercise.
Do you know the name of the numbers you have coloured in now you have done the sharing by $2$?
Do you know the name of the numbers you have left out now you have done the sharing by $2$?
Which multiplication table will you find these numbers in?
Which numbers have not been coloured in at all?
Learners could make a grid which goes up to $40$ or even $100$ adding $6$ and $7$ to the "red" numbers.
Suggest starting by making the table to use. Then colour in the numbers counting in $2$s omitting $2$ itself.