I've been having a lot of fun playing one of my Sims who I put on the Criminal career path.  It all started back when she had her birthday to Teen, and on a whim I selected the "Kleptomaniac" trait for her.  Muahaha!  

Next thing you know, I was keeping her up at night just so that we could go out and swipe stuff.  She's on level 7 of the Criminal career path now, and still climbing!  Here's some nitty gritty information about what it takes to become a successful Criminal.

The core skill for criminals is Athletic.  If you want to start grooming your criminal young, have them work on the Athletic skills!   There isn't much you can do for babies or toddlers, but children can play tag, go swimming, and play catch with the football.  Teens can work out just like adults, using the treadmill, weight bench, swimming pool, stereo, or television.  Teens can also go jogging.  

A word on jogging: it took me a little while to figure this out.  Whereas in Sims 2 you would just click on your Sim and tell them to "go jogging," it takes a little more work in Sims 3.  When I want to send my Sim out for a jog, I switch to map view, find a good turn-around point, and click to zoom in.  Then I click on the ground and tell my Sim to "jog here."  Then I click on the ground in front of their house and tell them to "jog here."  If you just tell them to go home, most of the time they will hail a cab!  I guess I can't blame them, but it kind of defeats the purpose.

Kleptomaniacs can steal things when no one is around.  Send them to a public lot in the middle of the night, be sure you're alone, then click on the ground and tell them to "Swipe something."  Your Sim will swipe some object and put it into the family inventory.  (In Buy Mode, click on the third bottom-most tab, the cardboard box below Items By Room and Items By Purpose.)  

She and I have built up quite a collection of public garbage cans this way!  Your Sim can also steal things from someone else's house, should they find themselves alone in a room.

The Criminal career path is unique, in that it has a branch halfway through.  When your Sim is promoted to level 7, you have to choose which path you want them to take: Evil, or Thief.  If you choose Evil, you will need to boost your Logic skills.  If you choose Thief, you will need to focus on getting accomplices.  When you reach level 10 on the Evil career track, your Sim will develop a permanent red glow.  Sims who reach level 10 on the Thief track will get a golden fox statue which gives +25 to your mood for 8 hours.

One down side to the Criminal career track is the possibility of getting caught and sent to jail.  This happened to my poor Sim once.  She spent the night in jail playing dominoes to boost her Fun score. When they released her in the morning, she practically fell asleep right there on the front stoop of the court house!  Sheesh!