Harriet
This is a Pattern for a round-neck Cardigan, Beanie or Bonnet, and booties.
The 16" 0-3 months size is made using DK yarn with 3.25mm & 4mm needles.
The 18'' 3-6months size is made using DK yarn with 3.75mm & 4.5mm needles. You will need 150g of DK yarn for each size. I used Sirdar Snuggly DK.
It can also be made in Aran yarn using 4mm and 5mm needles, following the 16' size pattern, which makes the items approximately 2 sizes larger.