The SIMS 2 requires administator right to play, you can find this info from EA web site. I also tried with my duaghter, but nothing. A lot of games are just the same.
To aviod your kids mess up your system is to install two copies of XP on different parition and make them hidden from each other, so you have two "virtual" PC. In fact, you can just make a new partition and clone your current XP to that partition and use a boot manager to select which one (either super dady XP or cool kids XP) to load when you swtich PC