the numbers in paren's? for different sizes.
newborn heads are about 16 to 17 inches,
by age one, most babies have 17 to 19 inches head,
by age 2, kids heads are 95% of adult size
(adult heads range from 19 inches to 25 (or more!) )
the different numbers are for different sizes
small is the first number, (medium, large)
you'll have to read the pattern to see how they define medium or large..
in some patterns you can find many sizes --size 2 (size 4, size 6, size 8, size 10, size 12) which might be expressed as
70 (75, 80, 85, 90, 95) !
a good practice is to first copy the pattern, then highlight or circle the correct number for the size you are making.. (before you start knitting!) then if you want to make the pattern again, your original is not all marked up.
with only 3 sizes, its not to hard to keep track.. (especially if you are doing the size outside the paren's)!