aaah OP i also love dental care by owl city!! a bunch of his songs are littlespace content for me, plus he did a side project under a name called sky sailing which you HAVE to check out! they're all so soft and child-like and perfect for lullabies.
another great artist for lullabies is called twinkle twinkle little rock star. they do these perfect soft covers of common songs of alll genres - emo, country, rock, metal, pop... everything! so it's already familiar to you or your little from the first listen.
i actually have put a bunch of my favourite littlespace songs into a playlist so i can just press play when i need it! there's a mix of fun/cutesy pop, dark pop (melanie, ofc), lullaby songs, disney songs... the whole load! you can find it here:
enjoy~