Might be moth caterpillars or slugs. Bacillus thuringiensis or called BT for short is a safe treatment for the various common caterpillar "worms", it can be found at good garden nurseries.

Late season grasshoppers can be a problem here as well as various caterpillars (there may be one in the picture along the main vein of the center leaf, very well camouflaged). If it's slugs I suggest going out after dark to inspect the plants with a flashlight.