What do we love about the KneeGuardKids Footrest at Saunders & Smalls Car Seats?
The footrest helps to relieve pressure on the child’s ankles when forward facing in a high back booster. It helps to reduce and numbness and improved blood circulation with adequate support for the legs, positioning them in a comfortable 90 degree angle. 
With your Small sitting more comfortably and supported there is less chance of them resting their feet in unwanted positions, such as on the back rest of the seat in front, up on their high back booster, sitting cross legged and slouching. Therefore as they’re sitting more comfortably they’re in turn sitting more safely.