They're held in place by seat belts. The seats are adjustable to fit the child as he/she grows. My children absolutely love them! They're not baby seats, though. I forget the exact weight requirement, but I'm sure it's easy to find.

 

In hopes of avoiding a misunderstanding, the ZO6 isn't mine.

 

I'm sure my 5 year old boy will like it like he likes to ride the evo all the time but he might release the seat belts while I'm driving.