I want to find some manga of any kind of genre that contains romance between young characters (typically under the age of 14).
It doesn't necessarily have to be the main focus of the plot, and the romance doesn't need to be explicit. It could just be a cute friendship, instead of actual romantic feelings. What I absolutely DON'T want are age gaps, NSFW, and most kinds of ecchi stuff.
I also don't really like those with 90's romance art styles (like those from Kodansha-published works).
Here are some examples of what I'd want to see:

Aragane no Ko: Mostly about fights and action, but there's a rivalrous friendship between the MC and a girl around the same age as him.

Tongari Boushi no Atelier: Roughly the same thing as the first one, but it's more of an implied romance than a friendship.

Jijou o Shiranai Tenkousei ga Guigui Kuru.: More of a slice-of-life romance, with no action or fantasy involved, but the premise is roughly the same.

Sorry if I sounded weird or picky, I really hope that more of those exist!

Hatsukoi to Taiyou if you don't mind shoujo. Both main leads are grade schoolers in modern Japan.

Tearmoon Empire Story another shoujo, this one is actually fantasy manga. The MC goes back in times, back when she was still in her early 10s. The romance wasn't that apparent for now.

Nekota no Koto ga Ki ni Natte Shikatanai. yet another shoujo. This one is actually a bit similar with the first one, both leads are grade schoolers in modern Japan.

Himeno-chan ni Koi wa Mada Hayai seinen, another romance manga between grade schoolers.

Sorry if these wasn't what you're looking for, i honestly haven't read those manga for quite long time. You should try using advanced series
search, maybe you'll find what you want. I just recommend the ones that i've read, so i might missed many manga.

I've read both Hatsukoi to taiyou and Himeno-chan, and both of those were quite good! I'm gonna try and read the other 2, thanks

There is a manga titled 14-sai no Koi 🙂 It barely fits into your description.

I read it before. The story was pretty good, but I didn't really like the art style.

I'm currently reading it, I'm liking it so far!

Thank you!