Ok, so I remember some time ago I came across this really cute manga about (surprise) 2 guys who end up having to take care of one of the guy's older sister's baby. I completely forgot about it until I downloaded Dangerous Pleasure's Jigoku Meguri Vol 2, and in the 3rd Chapter, found an image done by the mangaka. Or at least what I think is her art. This is honestly the only reference I have, thanks in advance.

Yo, there's a yaoi section. And it might either be one of the stories in Love Together or Seito no Shuchou Kyoushi no Honbun.

Failing that, it might one of the titles here: http://www.mangaupdates.com/series.html?category=babysitter&genre=Yaoi&perpage=50

Moved to Yaoi/Yuri~

Dekichatta Danshi