I think it is up to the software whether it installs itself for all the users or only for the current user. What you can do is delete all the shortcuts for that software from all the other users except yours.

I nice trick is to install the programs to a special folder, and then set the permissions for that folder so that only your windows account can execute programs from it. (DO NOT do this for your Program Files Folder).

when you install the programs go to the each user account and any icon associated with your programs. then go to the default user folder and remove what ever you don't want other others to have.
next time you are installing a program use custom setting and IF you get the option to install for other user choose just me.

any admin acct can move all over the computer in and out of each others file and folders unless special permissions are setup or the kids are on a limited account .I remove customers passwords all the time through the safe mode admin account ,that is not passworded because the average user doesn't even know that its there . so just simple removing of shortcuts doesn't stop the computer savvy kid! fro musing any program on the computer .

option i have suggested to a few people was a couple of removable harddrive trays and 2 hard drive one for the kids and one for you .