Yes, they can
Girls can become pregnant after receiving their period
750 000 a year.
Yes, many eleven year old girls are reproductively mature. If they are sexually active they can get pregnant.
All pregnancies in the US, or anywhere else, are girls.
850 000 get pregnant a year so on average that should be about 70800.
No, they cannot because girls cannot get each other pregnant. If you are asking whether a 13 year old can get pregnant by a thirteen year old boy, then the answer is 'yes'. If he is producing sperm and she is producing eggs and they have sex, it is possible for her to get pregnant.
Yes - there are recorded cases of 11 year old girls and younger being pregnant and giving birth.
all the ones who decide to have unprotected sex,
Yes, any early teenage or pre-teen girl can get pregnant if she is menstruating and sexually active.
varies with individual genetics but 8 year old girls have given birth
Certainly not at age 14. They have not demonstrated that they can take care of themselves.