I know this is a somewhat odd request. But are there any manga that have the dealing with...

Love so life (shojo)

Usagi Drop. Best slice of life

sorenari ni shinken nandesu. yaoi. if you want

http://www.mangago.me/read-manga/my_girl_sahara_mizu/

And then everyone got the biggest surprise of their lives when she grew up.

Faster Than a Kiss (involves raising a child but it's a side plot to the romance)
Yarou Wedding (yaoi)
Nan Eomma Nun Appa (manhwa)

http://www.mangago.me/read-manga/chichi_kogusa/
http://www.mangago.me/read-manga/hotman/
http://www.mangago.me/read-manga/flat_aogiri_natsu/