Pyramiding is caused by too much protein in their diets. I would be very suprised if your turtles' shells were pyramiding, because they're still hatchilings. It's not that the shape of the shell is like a pyramid, but that the individual scutes on the top of their shell is layered. If it gets really bad, then yes it does look like a pyramid.
I adopted my two males, and they were only fed pellets for the first 2 years of their lives. So their shells have some minor pyramiding. This cannot be corrected, but by providing them with vegetables and fruits and varying their diet more, I have been able to stop the process. Here's a picture of two of my turtles basking together. See how the one on the left has kind of a bumpy shell, while the one on the right has a smooth shell. Napoleon, the one on the right has been fed a good, varried diet, while Jebediah, on the left has some minor pyramiding.
Here's a pic of Ezekiel's shell. He was also shedding at the time, though.
Actually, since he was shedding, you might be able to see it a little better. See how the scute that is peeling off is so much smaller than where the other scutes are? There's all those layers of scutes on his shell.
So, if your turtles do have some pyramiding, then add more veggies into their diet and cut back on the protein and pellets. Like I said before though, it's hard for me to imagine that your little ones have pyramiding. Hatchlings diet is mostly protein because they're growing so fast. It takes a while for pyramiding to develop.
Hope that helps.