Ok here it goes.
1- I chalked my tires in the garage
2- I aired them down so the entire lug was touching
3- ran over some building paper (you want a good 4 feet, the more the better)
4-continue over the paper, do not back over it a second time!!
5- patiently cut out the chalk marks on the paper. I put the paper over some cardboard to save my blade and act as a good cutting board
6- pick a point on the edge of a lug or somewhere that you can line up to stay on your level line, line it up and tape the template up
7- now use some push pins in the tread "voids" to keep the template tight to the wall. I used one or two about every 6"
8- spray the paint in, but not too heavily. Drips are bad, and bogging up your template is worse! You may have to let your template dry every 3-4 times to prevent smearing
9- when moving the template it is important to line up the tread with matching lugs to make it look consistent. On my Iroks it was every 5th outer lug.
10- Show it off and hope your kid likes it!! Good luck!!