Recaro Young Sport works as:
1) Harness (20-40lbs up to 40in. tall)
2) Booster (30-80lbs 37-59in. tall)

As the child grows, the Young Sport’s headrest adjusts to five different height positions.[...]

Graco Nautilus 3-in-1 car seat can save you the trouble of changing three different car seats.
It will accompany your child straight from the rear seat to backless booster. [...]