Those innocuous little ramps I used to jog up are damn steep when you're propelling your entire body weight plus 20-odd pounds of wheelchair up them.
The shiny metal rail is lovely for keeping your hands clean, as opposed to propelling yourself using the wheel itself. However, that shiny metal rail gets very slippery in the rain.
A five-year-old pushing a wheelchair can get you over small door sills and bumps in the sidewalk. A six-year-old pushing a wheelchair can send you out in the street in front of a semi lickety split.
In a group containing three or more children, it's best to have a timeshare plan arranged ahead of time for who gets to push the wheelchair when.
Foot rests are nice and all, but when your wheelchair decides to start drifting to the left with every push on the rail, it's really handy to have your feet available to correct your course.
Bicycle-type pegs on the back of a wheelchair would be awesome for carrying small children who don't want to walk any more.