You will need

Cardigan
0-6 months (16in Chest) - 2 x 50gm Balls      
6-12 months (18in Chest) - 2 x 50gm Balls    
1-2 years (20in Chest) - 2 x 50gm Balls        
2-3 years (22in Chest) - 3 x 50gm Balls         
4-5 years (24in Chest) - 3 x 50gm Balls         
6-7 years (26in Chest) - 4 x 50gm Balls          

Cardigan with Collar
0-6 months (16in Chest) - 2 x 50gm Balls
6-12 months (18in Chest) - 2 x 50gm Balls
1-2 years (20in Chest) - 3 x 50gm Balls
2-3 years (22in Chest) - 3 x 50gm Balls
4-5 years (24in Chest) - 4 x 50gm Balls
6-7 years (26in Chest) - 4 x 50gm Balls