Very vague description. I haven't read it, but read part of the description off of its entry here or on some other site.

The gist was that some kids or brats were faced with a new babysitter or housesitter coming, as planned by their parents or parent. Then she turns out to be a very pretty older girl. University student? Or maybe closer in age.

Specifically remember the words "pretty", maybe "older" or "girl", and "brat" or "prank".

Art is probably not Josei or Shoujo.

I'll check all suggestions and their attached recommendations.

Tried searching on MU for the Babysitter and Childcare categories but nothing has a matching description :/