I figure out my guage, measure the child, and figure out how many stitches to use (sometimes I'll look up sizes vs. # of stitches on other people's patterns). Then I start at the top and work my way down. I knit in the round and do about 2 inches of rib at the top. Then I add a few short rows in the butt area. Knit until the crotch (I usually make that part longer than you would think you would need). I add a few extra stitches (maybe 8) to the last row, then I split off for the legs. I split the legs, putting half -10 stitches on a holder. I save 10 stitches, more or less, in the crotch, on the front and back center and graft them together for a seamless seam (that's where the 10 stitches from the holder go, and then obviously the other 10 come from the needle side). I don't graft together though until my legs are finished. I switch to dpn's and continue until my leg is as long as I want it, then I add more ribbing. Pick up the stiches from the holder, finish that side like the first. THen graft the seams. That's it! It's soooo easy, one of the first things I knitted. I've made a ton, and they fit very well. My mom has made a few and put in an elastic waistband. Some people think that the elastic gets nasty, but mine haven't. You can also easily make shorties the same way.
