Your daughter is one confident, smart, sassy chica. (OK, sometimes a little too sassy.) Make sure her bones are as solid as she is. Research on kids' health shows that girls ages 8 to 14 who take a 150-milligram magnesium supplement twice a day have stronger bones by the end of just one year. Sure she'll still have a sassy mouth, but she'll be using it to thank you when she's 60.