These dungarees are part of a Christening set for a boy, but they can also be worn by girls.
The bottom edging for each leg is worked first, and the leg is then knitted up to the crotch. After the crotch shaping, the stitches from both legs are worked together to the waistband. After the waistband has been worked, most stitches are cast off, leaving the stitches for the bib. The bib is then worked, followed by the two straps.
The dungarees are very stretchy and will fit a wide variety of sizes. They will be looser on a smaller baby.