perhaps they cannot make you at birth however, you can't take the deduction without one.If you want to claim them as a dependent. They CAN NOT make you get your child a social security number
http://www.ssa.gov/pubs/EN-05-10023.pdf
Must my child have a
Social Security number?
No. Getting a Social Security number
for your newborn is voluntary. But, it
is a good idea to get a number when
your child is born. You can apply for a
Social Security number for your baby
when you apply for your baby’s birth
therefore you will have to apply at some point between birth and filing of birth year.