Normal Kitten Weights

My foster girl had kittens on January 22nd, 2013. On the 23rd, all kittens weighed between 5.2-5.8 ounces. Yesterday, they all weighed between 8.8-9.6 ounces. Today, they weighed between 12-13.2 ounces. This seems really big to me for kittens that are not even 4 days old yet. Mom fecal tested negative while pregnant, and none of their bellies are distended or look abnormal so I don't think it's worms. All are eating well as is mom, who is on a high protein free feeding diet.

Is this something I should be concerned about?

Are you sure the scales are correct? 13.2oz is 374gm - the size of a 3-4 week old, they do not look that large in the photo

Your birth weight of 147gm (5.2 oz) to 164gm I'd suggest is also incorrect. Newborns are 80-130gm normally, and i'd think a c-section would be required for kittens that large

Agree with MM, I think you have a weighing problem.  Look for a cheap set of digital (electronic) scales that weigh in grams.  Although you normally use ounces grams are better for kittens as no decimal points will be involved.  A normal weight gain per day is 10g or more, and 10g is just over 1/3 ounce.