When did you switch your toddler/preschooler to a booster seat? at 3 1/2 we just switched DD1 to a 5 point harness booster that will switch to a high back booster and then a seat booster when ready. I think she was ready even though she's still harnessed in, I wanted her to get used to sitting lower. She loves it which I was surprised. We moved DD2 to her old convertible car seat.