I'm not sure how I should age the babies, they were an over winter nest so I have no idea what the exact hatch date was. They came up May 8th and I've been caring for them since.
If you scroll down the page there's a thread I started called "Baby box turtle growth question" at the time the largest was 2 and 5/8th", it's a tad bit bigger now. The smallest has also grown slightly.
I suspect the largest one will be near 3" by the time they all go outside. Growth is dependant of food, more protein can increase the growth, however it really needs to be balanced out and plenty of calcium provided. I realized today why the largest is bigger than the others, when it hears me move around anything in the cage it pops out looking for a meal!
At the time the babies came up I had been caring for the parents for a little over 3 years, unfortunately the female was stolen and the pen trashed shortly after, I suspect by a couple of kids. I was never able to get ahold of them or their parents. The male is hibernating outside in his 8'x12'x4'H pen.
Lesson I learned there was never underestimate that people may come into your fenced in backyard.