From some of the comments on Ravelry, there were a few that said Rib-A-Roni ran small. I made the youth size making gauge at one rib per inch for a 3 year old and it is small.
Helen's Hat is Spiralini adapted for an 18 month old: http://www.ravelry.com/projects/myshellyknit/spiralini-hat
This one runs large due to the slouch and my gauge. I started with 72 stitches (4 spi) in the ribbing and then increased to 80 stitches for the body, knitting even for a total of about 5.5 inches for the length before decreasing. The decreases are based on a 10 stitch repeat so there were no further changes. If I had been thinking, I could have changed the swirl to a 8 stitch repeat. That would have resulted in more sections but the swirl lines would have lined up with the ribbing like the designer's. Helen's curling vines are crocheted.
Indy's hat is has a roll brim with 64 stitches (4 spi). After the 2 inches of deep orange in stockinette, there is an 7x1 rib (knit 7 stitches, purl 1). Total length before decreasing, is 5 inches. This hat runs a bit small for this 9 month old but I have enough yarn to make another one for next year. ;)
Hopefully, Callum's and Helen's hats will fit and we'll have a Pumpkin Patch Kids picture.
Update: The day for the cookout was too warm for hats. Callum politely refused to pose with Helen and Indy, so the picture below is my consolation. Callum's hat ran small and Helen's is a bit large, most likely she will be able to wear hers next fall, too.