So, for a little comparison (which means absolutely nothing, and no parent should compare their children). Perhaps comparison is the wrong word... for fun, here are some videos of the other kids when they started walking.
MJ walked at 9 months old just like Sheila. This was not the best video of it, but this video also very well captures his chubbiness.
Joey was also a pretty physical and atheletic kid, but didn't walk until right at his 1st birthday. I think some of it had to do with his toe which was a little special when he was a baby. I have a few other videos of Joey walking, but this one also captured our sweet MJ when he was 3.
9 month stats:
MJ - didn't have any b/c he was in Bangkok, but here are his 6 month
MJ (6 month) W:27lbs 2oz H:28 3/4 inches
Joey (9 month) W:27 lbs 10oz H: 31 tall inches head:18 1/2
Sheila (9 mth) W:20lbs 6 oz H: 28 1/4 tall inches head: 18 1/4
Sheila is in the 80% for height and weight and 95% for her head size (guess she's smart too)
MJ and Joey were both over 20lbs by the time they were 4 months old. So Sheila is still small to me!