My son was almost 13 this year, got his first buck in the 33 junior hunt. Just a spike but he didn't care. He also got his first javelina with his bow in Jan. You'll have a great time out there with your son, well it will be a toss up if you or him are having more fun.
She needs to shoot whatever she shoots the most accurate. My hunting partners boy is 10 and shoots a .270 with a muzzle break, the boy hates to get kicked.(but loves the 270 with the break) My son also shoots a 25-06 with a muzzle break. Muzzle breaks work great for smaller people or people who don't like to get kicked hard. Women typically fall into this catagory. Whatever you get here, put a break on it.