We do tiny bits of fresh dark green lettuce and other dark greens...I try to make sure that they are tender (young) greens as they seem to be able to eat those better. And thawed peas. I waited until 3 weeks for the peas but that young I think if just smash the pea you can offer it. I know there is more you can offer them but we stick to this mostly because it's actually food WE eat so it's already here.
My ducks love kale and mill worms. People are always saying their ducks love peas but mine weren't impressed all that much with them. Our Rouens will eat almost anything if you float it in water. They really went after cucumbers yesterday after I floated them in water. They didn't seem all that impressed with them before that. My Peking is a little more picky about what she eats, she really didn't care for the cucumber. We don't eat kale but my grand daughter seen it at the store and had to get them some. We just hold the stalk and they just break off what they want.
Just keep in mind they have to have grit before they start getting veggies, because that's how they digest their food. You maybe aware of the grit thing already but I wasn't so I really appreciated this advice. I also just realized you have babies so anything will have to be more finely chopped or mashed.