Shonen maid. Is about an orphan boy who moves with his rich uncle and becomes his maid because he's a lazy ass who never cleans anything. There are other cute shotas shotas too (like an idol group).
Not to confuse with the hentai OVA with the same name and similar premise.
Uchi Tama is good too, although it has less shotas and more older boys. It's an anime about cute kittens and puppies that replaces the animals with anime boys (and two girls) and with a shota cat and a shota pup as the protagoninsts. Everyone is so innocent that having lewd thoughts of them can make you feel guilty.
As other anons mentioned, Toilet-bound Hanako-kun is another great title. It's sometimes dark and sad like they mentioned, but the happy and wholesome parts make up for them. Besides, the tragic backgrounds of the characters (because Hanako isn't the only one with one lol) is what makes the interactions between them so good, that and Hanako being a cute dork.
About Made in Abyss, the basic premise is about a loli explorer (Riko) who meets an amnesic shota bot (Reg) who came from the bottom of a huge hole (the abyss) and then decides to go there to find her mom (who went there long time ago because reasons). During the journey they find all kinds of characters and creatures, like a furry thing (Nanachi) that decides to travel with them. The manga is full of suffering (they can't even leave the abyss because it makes them bleed from every hole) and blatant fetish pandering (Riko being naked and/or hurt, constant references to Reg's dick and butt, Reg probably being a furry, loli pee and poop, etc), but once you get past these pleb filters you find a really cool manga with a great world and character design.>>3429271
Hanako-kun isn't as dark as they want you to believe. Don't give up on the manga just for that.>>3429288
Assassination Classroom is great, and Nagisa acting like a boy despite his feminine appearance was even better (I'm tired of ultra feminine traps).