Okay, I'm going to try to get a bit more in...
Again this will look like an hour glass shape, but one end will be a lot fatter than the other. The fat end will be the back/bum side.
I knit mine from the top front, next the crotch, last the back.
So the top is where I cast on (about 4-7" wide).
I knit in 1x1 rib for 2-4", then in st st for a few more, then I increased over a few rows so the piece was a couple inches wider overall.
When it's somewhere btwn 4-7" long (depending on how big you want it) and 6-8" wide, I began decreasing until it was about only 4" wide.
Continue in st st for about 4-6". This will be the crotch part.
Increase again over the next several rows (about 4" of length) until the piece is quite wide, prob 10-15" depending size you want it). This will create the extra wide/room needed for the bum.
Now decrease again over the next several rows (about 4-7" of length). This will bring the top in to make the narrowness of the waist.
When it's as narrow as it needs to be (4-7" wide) cont in st st for a couple of inches. Switch to 1x1 rib for the last 2-4" for the waist band. This should be same amount you did at the beginning.
Bind off loosely. This may go without saying, but you may want to do one of the special bind offs so it's really loose, like where you add a stitch the previous row http://www.socknitters.com/Tips/stretchy.htm .
Sew up the wide part/sides.
Now the cuff. Thought you were done, huh? Pick up stitches around the leg opening. I would try really hard to make sure this part is loose, loose, loose. This is one place where if it's tight, it will be unuseable. Knit a cuff in rib knit. Prob 1x1 will work. I haven't done this part yet on mine (and I ran out of yarn and am waiting for it to come in...). Continue for about 3 inches. Bind off reallllly loosely. Roll up cuff so the whole cuff part is twice as thick. And sew it down. There's prob a groovely way to do the bind off and sew it in one fell swoop, but I don't know how to do that yet.
Now take a picture of your masterpiece, send it off and tell your friend to join a knitting group, LOL!
Now for a bit more details:
To make sure you have room to sew up the edges add 1/2-3/4" inch to the width thru the waist and hips.
I have to use a smaller gauge needle for my rib or it is too loose and baggy.
Soakers need more power in the crotch and bottom. This is b/c its where the baby pees, of course, but also where they will be sitting so the thickness prevents wicking onto clothes and Mama, etc. You could do this by using one of these ways as soon as you begin decreases for the crotch: ribbing, sks, cable, use 2 strands, double knitting.
A GREAT soaker, prob the best out there is an Aristocrats. If you can get your hands on one, you prob get an idea of what to do from there
http://www.greenmountaindiapers.com/woolcompare.htm (at the bottom is a pict of another good brand, Disana).
http://www.aristocratsbabyproducts.com/diaper_cover.html (the manf website).
In general you need a tight fabric, so use a small needle for the yarn. I normally use a US7 with worsted weight for a hat, but I would use prob a US3-5 with worsted for a cover. If you can see thru the fabric it prob isn't tight enough. Or if you can easily pull apart the stitches and make holes, it's too loose.
I would NOT use a Superwash wool. Ever. I'm not sure why PP recommended that. Any superwash wool is going to have all the lanolin stripped away and the lanolin is critical to making it work. It prevents leaking and odor. It will need additional lanolin applied before using and every so often btwn wearing. http://www.thediaperhyena.com/woolscool.htm There's more info here than you prob care for, but you can just read what you like. It will need to be hand washed OR super gently machine washed and you can only use wool wash like Eucalin or another brand. Woolite will ruin it ( it actually removes oil taking the lanolin with it. Good for clothes, bad for diaper covers.) B/c it's a detergent, it can also cause unwanted felting.
If you have any questions about the wool's softness, most will get softer after repeated lanolizing. I like the merino the best so far.
Since you won't use superwash, consider that this will eventually shrink/felt a bit, if only from the baby constantly wetting it and the friction of the baby crawling and walking around in it. So I would make it an inch or two bigger all around than you think you'll need. Also, it will give the baby room to grow.
Mine is for my 3 1/2 yo, about 39" tall and prob 35+#, fairly big for her age. My finished soaker (laid flat before being sewn) will be 7" at the top/front, increase to 8.5", decrease to 5" (for the crotch), increased to 15.5" at the widest in back and decreased to ~12" at the top of the back. The whole thing will be ~18" long. Most kids will wear a much smaller soaker.
HTH! And be assured I will post a pict when it's done!!! :cheering: