I do have three car seats across the back of my Sedona but we did try a few before we found a model that worked. My problem is that I care for a three and a half year old who is quite big for her age and really too big for these "baby" seats with five-point harness, but also not to be trusted in a booster seat with three point harness - always wriggling out, undoing the buckle etc and generally putting me on edge trying to watch her whilst driving. Does anyone know of a seat with five point harness for bigger kids - maybe geared for children with special needs?