Karen, that does look like rotting rather than something eating them. Although woodlice damage can be hard to notice, so that is just possible. You would also see serrated edges to lower leaves, where woodlice nibble.
Yes I suspect overwatering as that can make stems rot, very quickly too. Young plants are especially prone.
I plant also at about two, perhaps three large leaves.
Possibly you had previously overwatered the plants in pots. I keep mine half dry, so the pots are never heavy if you lift them.
