It's been quite a while, and I've really enjoyed all the recommendations given so far. However, as this is one of my favorite tropes and a long time has passed, I'm hoping that there are now more that people can send my way. So please, let me know if there is anything not already suggested =]

Ai towa Yoru ni Kizuku Mono
Ake Nure Goyou ni Furu Yuki wa (chapter 5 - though there is drama)
Home (TSUYUKI Yuruko)

Boku no Shiru Anata no Hanashi (older one is dating the younger one's mother when the younger one is a kid)

Not sure if omegaverse is your cup of tea, but Sayonara Alpha has this exact trope!

Stay Gold (Hideyoshico) is probably in that category. I'm still reading it so I don't know if there will be a time skip, but there is a kid crushing on an adult.