I appreciate your predicament. I was at the same point with my boys several years ago. What woke me up was my son's statement "Dad, are we going to be able to see the car before the race?" The body was CNC machined, wheels turned true, weight to within .001 g, etc. We placed 2nd. to a car that was built entirely by a 10 yr old! IMHO, help them get the weight right, but let them do most of the work.