You will need

Shawl Collared Cardigan
2-3 years (22in Chest) - 3 Balls
4-5 years (24in Chest) - 4 Balls
6-7 years (26in Chest) - 5 Balls
8-9 years (28in Chest) - 5 Balls
10-11 years (30in Chest - 6 Balls
12-13 years (32in Chest) - 7 Balls

Round Neck Cardigan
2-3 years (22in Chest) - 3 Balls
4-5 years (24in Chest) - 4 Balls
6-7 years (26in Chest) - 5 Balls
8-9 years (28in Chest) - 5 Balls
10-11 years (30in Chest - 6 Balls
12-13 years (32in Chest) - 6 Balls

3.25mm and 4mm Needles
2 (2 : 2 : 2 : 3 : 3) Buttons for Shawl Collar Cardigan
3 (3 ; 3 : 4 : 4 : 4) Buttons for Round Neck Cardigan