If the ratio says there are 3 boys, and 7 girls it shows us that there are 3 boys every 10 children, and 7 girls every 10 children. Since, we need to find out how many boys there are for 20 children total.
As a result, we need to multiply both amounts by 2.
3 x 2 = 6
7 x 2 = 14
This means, if there are 20 kids in total, there are a total of 6 boys.
