Can someone tell me how to make a cuff to cuff pattern fit a baby

I made myself a basic cuff to cuff shrug for myself and I love it. Just knit one cuff , increase sts , then work across in stockinette stitch until length is done ,then decrease sts and make cuff and your done.
It was unbelievably super easy. I now have to make a baby gift for a friend and was wondering if someone could tell me how to make the same pattern ,but for a 6-9 month baby .
I know it can be done, but I don’t know what the cast on number would be.
Is there anyone that could help?

You’d have to figure it by measurements. Here’s a chart for baby measurements, you’d need to add a little more for some ease. Lion has a baby hoodie that’s knit cuff to cuff which would give you some numbers to work with. I made it and left off the hood because I didn’t have enough; the hood is knit separate and sewn on anyway. The sleeves are a bit short I think, I knit it big enough for a size 2 and made the sleeves long enough to roll up a little so my GD can wear it a bit longer.

Thanks Suzeeq, I like the hoodie, I’ll have to make that one also. Thanks for the like too