After using a birthday cake and having a birthday party for a toddler, that Sims will advance to the preteen life stage. Preteen Sims can become Teenagers by completing Osiris's teen mission.
The preteen life stage is only available in The Sims FreePlay. It is similar to the Child stage in other games.
Toddlers
Completing A Quest for Toddlers, available at level 12 after completing The Mysterious Island quest, unlocks the ability for babies to grow into toddlers and the ability to adopt a toddler.
Hobbies
The Community Center is mostly for preteens. They are able to learn karate or ballet there. However, there is also woodworking benches for Adult sims. Preteens can also learn diving.
School
Your preteens can also earn Simoleons and XP (experience points) by attending school.There are three time slots available when you decide to send your preteen to school-- morning, afternoon, or evening. However, keep in mind that when you choose a time, that is the time your preteen is expected to go to school from then on... so choose a time that will work out to be great
The amount of money (allowance) and XP your preteen will earn from going to school depends on their grades. The higher their grade, the more Simoleons and XP they will come home with.
Your preteen can improve his or her grade by (1) going to school every day, as well as (2) studying with a Study Desk when they're at home. You can purchase a Study Desk from the Home Store, under the 'PreTeens' tab, for Simoleons or Life Points.