Measurements
Instructions are for 3 sizes:
2-4 years, 5-8 years, 9-12 years

Materials
Each source has a different list of suggested yarns.

The following are from the Wendy pamphlet:
Wendy DK with Wool
1, 1, 1 X 100 gram ball
or
Wendy Merino DK or Wendy Elegance DK
2, 2, 2 X 50 gram balls.

The following are from the Jarol pamphlet:
Supersaver DK or Sweet Brier DK
1, 1, 1 X 100 gram balls
Superwash DK
1, 1, 1 X 100 gram ball.