Looking for some easy to read books.

Hello, I have been reading again and am looking for some possibly middle grade or YA novels that are joyful and easy to read between my heavier themed, adult oriented books.

It would be nice for them to be shorter in length and not super dark, theme wise.

I already got Chronicles of Narnia and to the side of my main books, am reading Percy Jackson with a friend.

Fantasy and sci-fi are my favorite genres, but I've learned that most fiction is fine for me as well.

Right now for my "main" books I'm reading through The Greenbone Saga, Mistborn era 1, and The Keepers trilogy. I read them one after another, switching between the trio everytime. Sorry if I'm repeating myself, but I am looking for something between each of these books.

I've noticed that I need something not so serious and joyful between the darkness of the other stuff.

I am also looking for stories I can share with my nephews and soon to be niece if they decide they enjoy reading and stories, as they grow. I have three nephews, two are 4 years and the youngest just turned 1 in January, so he's got some aging before he is ready, while my niece is yet to be born.

Thanks!