Google "day care in high schools" and you can find some places where this is already taking place. Here are just a couple of the links:
http://www.d321.k12.id.us/~Central/daycare.html
http://www.booth.k12.nf.ca/guidance/daycare.htm (I particularly like the graphic on the top right side of this page
)
http://www.cbc.ca/news/story/1999/12...are991201.html (this one mentions the possible "deterrent" effect I mentioned earlier
)