I agree with the umbilical comment. Looks like mom took a little too much off. Don't think it needs a trip to the vet unless it starts looking infected. Babies heal pretty quickly so glad it's starting to look better. I've been trying to figure out colors for your babies. The brokens will be really hard because they don't have a lot of color. I'm seeing a broken black, broken tort or red, and maybe a broken shaded color I haven't figured it out just yet. It's annoying me lol