Baby's growing

I took Adora to the Doctor on Friday to be weighed and she was 9 lbs 13 1/2 oz. How do babies grow so fast? Sabian will be 2 yr old on Friday. Naomi's in kindergarten and loving it. I let Naomi and Sabian go to Grandma Kathy's for the weekend and I'd swear Sabian grew up a little more while he was gone. I'm sure he's already planning for the day he gets to drive a real car.