the tutorial says the child wearing it is 30ish lbs in weight. I'd say make one & see how large it is first.
here is the link
The baby that modelled the bapron was sitting up but I don't have a model (Granddaughter) who can sit up yet so I can't tell if it's the right size. A little bigger might sell just as well. Jan
Michelle, can you tell how big the pattern is? I didn't see it, so I can't help.
I have made lots of bibs in my time. I feel that you need several sizes. Babies grow and the need to cover them with different size bibs, do as well.