Buy a pair of thinning shears from a beauty supply store. Although you can thin hair with standard styling shears, the process takes much longer and is less effective with squirmy children.
Wash and dry hair. Clean hair is the best medium to work with when thinning hair at home. If you're giving your child a haircut, do so before starting the thinning process.
Brush hair into the normal style. It's unnecessary to apply styling products or use a curling or flat iron. Simply brush the hair into place. This shows you what areas are overly thick and require thinning.
Separate a narrow section of hair in the desired area. Use a comb to evenly part the section, rather than pulling out a ragged grouping.
Hold the section out straight. Open the thinning shears and place them around the hair, approximately halfway down the hair shaft. Close the shears, then reopen them and remove from the area.
Comb out the trimmed pieces so you can assess the thinning process. Move to the next section and repeat.