Wait so is those the kids in Delicos nursery when they’re older?

yes

Is this a sequal or something?

um sort of? it's basically its own story but it is related to the nursery yeah! you should definitely take a look at the original website, they have provided quite a lot of information on the anime, manga and the stageplay if you're interested

A spin off? I actually haven't read/ watched the original so I don't wanna get spoiled