Could it be pigeons or mice or when I first grew them there was some pest in the ground that used to nibble the leaves. I found that growing them in roof guttering until they were a good size, stopped the critters eating them. Some of my fellow allotmenteers cut the tops off clear plastic bottles and put them over the young plants until they grew but this was rather a lot of work.

If it's mice eating them, mouse traps will stop them. I caught 6 mice that had been eating bulbs and seeds in my garden. Not any more, they aren't!

Just looked back to last year when I asked the same question and it turned out to be pea weevils which nibble the edges of the pea leaves - a bit like someone punching a bus ticket - if you are old enough to remember that!