oskiwow - Welcome !!
I am sure Kinser has this down to a science, here is roughly the order of what I did with a young relative in more like 6-7 hours (going for speed) recently:
Initial Body Work
Sand Block to fit Silver Bullet
Mark Block
Drill Axle Holes
Verify Initial Alignment
Trace Car Outline, Weight Holes
Cut Out Car and Wt Holes
Install Any Weights Going Thru Car Sides
Sand & Patch and Put Aside Until Dry
Axles
File Axles
Sand and Polish Axles
Bend, Slot RR Axle
Coat, Lube Axles as Desired
Final Body Work
Final Sand of Car Body, Seal & Prime As Desired
Paint Car
Wheels
Sand Wheels (if Required)
Prep Wheel Inner/Outer Hub, etc. as req'd
Prep Wheel Bores
Any Final Wheel Prep
Final Prep
Weight Car close to 5 oz.
Set Initial Drift
Initial Lube of Body and Wheels/Axles
Test & Tune (if Possible)
Final Lube (if req'd)
Glue Axles
Box for Transport
Not that much different from what you had, just more details. Some amount has to be customized obviously for your rules, tools, available parts (i.e. lathed wheels) and products (e.g. bore polish) and obviously time frame and what your goal is. Young kids get along well with the water based acrylic paints which dry quick. Some of the more pro steps like tuning the weight placement are likely not practical for what you are talking about.
There are a lot of posts in different forums about Workshops, check those out, including the one from 5Kids (I think) in PWDR. Since I had 4 kids at home making cars most of the time, our house was kind of like a workshop. You need to think that way a bit to move along quickly - for example, I have a plastic box with enough compartments for pre-cut axle sand paper strips, string and polish. I would lay out piles of successive grit for other sand paper for the body work, anything to help keep the idle time down because young kids have limited attention span. I always had pictures for kids to look at for shape ideas, as well as paper drawings of the blank car with wheels on it that they could draw their own ideas on.
Along the way I try to tell them about why we are doing these steps. I try to finish with a classic 'do your best' mini-lecture about how anything can happen on race day, congratulate whatever kid wins, etc., and then tell the kid and the parent about not touching the car until check-in. I show the kid how to hold the car so that he can present it for inspection.
Hope that helps.