For this pattern you will need (50g Balls) :

Tank Top
0-6 mths - 1 Balls
6-12 mths - 2 Balls
1-2 years - 2 Balls
2-3 years - 2 Balls
4-5 years - 3 Balls
6-7 years - 3 Balls

Sweater
0-6 mths - 2 Balls
6-12 mths - 2 Balls
1-2 years - 3 Balls
2-3 years - 3 Balls
4-5 years - 4 Balls
6-7 years - 5 Balls

 Needles Needed: 4mm and 3.25mm
Stitch Holder