I was concerned the ones on the bottom may be molting, too, but I have watched them a lot, and they molt in the water column, above the bottom.
Also, it seems my heater maims them! I couldn't get the plastic-covered heater because it was out of stock, so I got the normal glass tube one. That thing gets HOT. My goodness. It scares me. They touch it and then they just sink and flop around.

Wode, get the plastic coated heater!!! Don't get the normal ones! Confirmed baby killer heaters.
Yes, I've told my husband a million times how much I appreciate his help.

I am very lucky. He doesn't even like animals except for cats.

But he's a good helper.
Thanks for the food suggestions. I'll have to try those next year if I get babies. I'm pretty much broke this month, and can't afford to buy stuff to experiment with. It's been a trip talking my husband into buying more stuff for them starting with the salt, and now this elevated sandbox thing. I doubt I could talk him into buying them more food. But maybe next year.
I think some babies may be into the third larval stage. I'll have to try to get pics today.