I absolutely love this pattern and want to knit it for my 6 year old. However, the size only goes up to 5t and she is much larger than that. I have Caron Simply Soft and would like to make the pattern fit up to a tween size. I'm confused as to how to do that. Any and all help would be appreciated! Thank you!
You may not have to increase the largest size very much--ribbing stretches A LOT.
However, with that said, you'll need to add stitches in multiples of 6 (since the ribbing is 3x3). As for the ear flaps, you might even be able to keep these the same size as the original pattern.
I would do a swatch (in the round and in 3x3 ribbing, of course) to find out how many stitches per 4 inches you get. From there, you can figure out how many multiples of 6 you'll need to add to get the size hat you want.
I don't think you'll have to add stitches or even go up in needle size, kids heads are pretty much the same until they're older. Measure her head, then subtract 2". Divide the number of stitches by the gauge you get and that should be close to the same size you need.