I wouldnt use the stripper wheel on anything other then a but of soft paint left behind after scrapping.
Thats stuff is still nasty and you dont want to fling even a little bit off w the wheel....
Stripper needs to go down in 1 smooth stroke. No brishing back and forth and no smearing it around....
Initial contact seals out air and re-brushing 'lifts' 1st coat and prevents it and 2nd coat from working quite as well.....
Do smaller areas on opposite sides. Apply, cover, move to the other side, apply cover and wait 20 min then go and scrape 1st side, then 2nd....
If its still not great results, apply, cover and wait 30min try again.
I think some have left it 12hrs or longer to let it really chew on the paint.
Also when covering, dont smoosh/wiggle or press plastic down too much. It might be doing the same as re-brushing and hampering effectiveness.
If all else fails to improve reaults (tried the flour trick yet?) step up to a nastier stripper, like airplane paint stripper. It is probably best not to let your son apply, help cover or remove it though.... At least not the 1st few times you use it. Rusto makes a good one, but I used the brand sold at my local auto parts place...