This is a boxy oversized fit so buy to size.

1-2 yrs  chest 37.5cm | Length neck to hem 30.5 
2-3 yrs  chest 38.5cm | Length neck to hem 33.5
3-4 yrs  chest 39.5cm | Length neck to hem 36cm
4-5 yrs  chest 40.5cm | Length neck to hem 40cm
5-6 yrs  chest 41.5cm | Length neck to hem 43cm
6-7 yrs  chest 42.5cm | Length neck to hem 45cm
7-8 yrs  chest 43.5cm | Length neck to hem 47cm