The Sims 3

This is a complete, detailed guide for the "Child Prodigy" achievement.

Before starting, make sure you have "Enable aging" turned off, or at least have the game set to Epic. This can be done by hitting the start button, going to options, and scrolling down to Sim Lifespan for Epic, and to "Enable aging" closer to the bottom. Also, High free will is recommended, so you can focus on the child while the parents do there thing.

1. First, you can either start a new game, with a baby, toddler or child( if you do this skip to step 5), adopt a child using the phone, or have a child in game with current Sims. I highly recommend doing this achievement with a kid you had with two Sims that are already well established and have the Life rewards of Steel Bladder, Dirt Defiant, and Hardly Hungry(purchasable under the lifetime rewards button under Sim Info). This will allow you to focus as much time as you can on the kid.

2. As soon as you have the baby, Buy a birthday cake in the buy menu (Entertainment>Parties), and have the baby blow out the candle(Make baby active Sim, then choose birthday cake.)

3. Now, in the toddler period, it is VERY IMPORTANT to teach the toddler ALL THREE toddler lessons, walking, talking, and potty training. Start with Potty training, using the "First Step Potty Chair" found in Kids>Furniture in the buy menu. You can only potty train when the toddler has part of his bladder bar empty, so pay attention to the toddlers bladder while teaching to talk and walk.

4. Once you have taught the baby all three skills(Note, if you do not teach all three, you will not be able to complete the achievement), buy another birthday cake and have the toddler blow out the candle. You should choose the Traits "Bookworm" and "Artistic". Make sure you have 40 Karma points available before you do this, and have purchased the "Stroke of Genius" Karma Power from the Challenge Shop, and have a computer available for your Sims.

5. Immediately active the karma power "Stroke Of Genius" for your child and have them begin "practice writing" on the computer. the lifetime wish of "Illustrious Author" SHOULD become available instantly. If not, continue having the child practice writing or painting until it becomes available.

6. Now, simply keep the child practicing writing and painting in it's spare time until the achievement pops! Remember to use "Stroke of Genius" every chance you get.

Note that you can get this achievement with a number of other lifetime wishes, I just found this one to be the easiest to set up for. If you decide to go for a different lifetime wish, make sure to choose one that has nothing to do with a job, as children can't get jobs.

Good Luck!

Edit: Note from Lt Davo. It helps to read painting books to your toddler to improve thier painting skills later in life, and helps ensure getting the writings/painting wish. Thanks for the tip!

Edit: It has been reported you may only be able to age someone one time with aging off. If you find yourself unable to age your child further, turn aging back on.

The method above is probably faster if you're staring with a fresh sim, but I couldn't seem to get it to work. I used a method I found on another website. This method, I would say, is faster if you have a child or teen sim that's lived in your household for some time.

For this method you need either a child or a teen. Like the other method, make sure aging is either epic or off. Continue completing wishes for your sim until you build up 10,000 lifetime reward points. Once you have them, hit . Use and to get to the Sim Info tab then hit and then to select "Lifetime rewards." Scroll down until you see "Change Lifetime Wish" and select it. The game will now give you five options to choose from. Choose your favorite and that sim will now have that lifetime wish. Do not choose a career, family, or romance based wish as you need to be an adult to complete these ones. From here, all you have to do is complete the wish requirements.

If you have any questions I'll do my best to answer them.

The Brady Bunch Strategy
This strategy will allow you to accomplish this achievement by hitting the game with multiple options. You have one parent/guardian and five potential teen prodigies.

List of usable lifetime wishes:
Chess Legend - trig: Computer Whiz, Genius, Couch Potato
Goal: Max logic and 5th level in pro chess
Golden tongue/fingers - trig: virtuoso, charismatic, great kisser, good sense of humor
goal: max charisma and guitar
Heartbreaker - trig: commitment issues, great kisser, flirty, party animal
Goal: have 10 romantic interests (regardless of gender)
Illustrious Author - trig: Artistic, bookworm, loner
Goal: master both painting and writing skills
Lap of Luxury - trig: mooch, snob, ambitious, kleptomaniac
Goal: family net worth of 100,000
Master of the Arts - trig: artistic, virtuoso
goal: max painting and guitar
Perfect Mind, Perfect Body - trig: genius, athletic, loves the outdoors, perfectionist
Goal: get to level 10 in logic and athletics
Perfect Private Aquarium - trig: angler, loves outdoors, perfectionist
goal: 13 perfect fish in fish bowls
Professional author - trig: bookworm, couch potato, loner
goal: 4000/wk in royalties
Renaissance Sim - trig: commitment issues, workaholic
goal: get 3 skills to level 10
Super popular - trig: charismatic, friendly, mooch, party animal, schmoozer
goal: 20 friends
Swimming in Cash - trig: mooch, snob, ambitious, frugal
goal: 50K in cash
The Culinary Librarian - trig: natural cook, vegetarian
goal: read every recipe book (requires max cooking)
The Perfect Garden - trig: green thumb, natural cook, loves outdoors, perfectionist
goal: grow 8 different kinds of perfect plants
The Tinkerer - trig: computer whiz, genius, handy
goal: max Logic and handiness

Note that "trig" is the mandatory traits. It means you must have AT LEAST one of these traits in order to trigger the LTW. You will also have to select alternate individual traits that best suit the role your prodigy will play during the game.

1. Start a new game.
2. Create a parent/guardian. There job is only to bring in money (plus it's a game requirement). Pick whatever you want for this but you will not be interacting much with this sim. For ease of use name the sim: Mom/Dad/ATM.
3. Create 5 teen sims. Name them after the lifetime wishes you're going to use (e.g. "Cook" if going after Culinary Librarian)
4. Pick your 5 lifetime wishes and pick the appropriate traits for your teens to accomplish it. (e.g. for Culinary Librarian you'd want natural cook, perfectionist, bookworm, green thumb/neat).
Note #1: Some LTW are much easier to accomplish than others. Try to pick LTW that complement with another one. For example Culinary Librarian complements both Perfect Garden and Private Aquarium because the fisher provides fertilizer for the gardener and cook. Tinkerer and Perfect Mind/Body also complement one another because the sims can practice chess together.
Note #2: The other important factors are location and speed of skill training. For example more next door to a place with a fishing spot is more productive for the Aquarium LTW. The community center with a garden works great for Culinary Librarian. Some skills are much easier to build up than others and/or require very little interaction. Cooking, handiness, athletic (workout to the cheapest radio) can all be built up rather quickly. Charisma can build up quickly but requires alot of interaction and throwing parties to build it up. Fishing, logic, painting, writing all seem to progress slower (exception being logic if you double up on using complementary LTWs that use the logic skill)
5. Start up the game, pick your home, and buy your gear: chessboard, water sprinkler, easel, radio, upgraded television, 6 seatable table, picnics table and grill (for parties), 5 single beds, 1 double bed.
6. Disable aging and stay on the mission. Do not deviate to do other major tasks and challenges.

So which LTW should you pick? Pick whatever you want. To the contrary, doing "max skill" LTWs is actually more time-consuming than objective-based LTW modes. For example Tinkerer takes longer to complete than Chess Legend. Handiness is the easiest skill to level due to the amount of opportunities you'll have to use it. LTWs (that aren't "perfect-based) such as Super Pop and Chess Legend should be easiest to achieve.

TL;DR Select an objective-based (that doesn't have a perfect requirement (e.g. "perfect vegetable"/"perfect fish")) LTW to complete this achievement the fastest.