This cute little romper is made using hdc stitches for the yoke then a granny stitch for the body and back to hdc for the crotch. There will be one button at the back of the neck to fasten and two buttons for the crotch.

Written in English US terms with abbreviations for UK

Sizes
Preemie to fit 13 inch chest
Newborn to fit 14 inch chest
0-3 Months to fit 16 inch chest
3-6 Months to fit 18 inch chest
6-12 Months to fit 20 inch chest
1-2 Years to fit 22 inch chest

Materials
dk / weight 3 yarn (I used paintbox simply dk) (more will be needed if making the optional sleeves)
4mm hook
3 x 10-15mm buttons

The pdf is 23 pages with each size written separate including pictures.