As I mentioned before R. is a slimmer baby. Around the waist he wears 0-3 months, but in length he needs closer to a 6-12 month size. The best solution seems to be to sew bottoms for him.
To make these pants I took a pair of pants he had and folded them down the middle, with the outsides of the legs meeting. I then traced those pants onto white paper, adding about 1/2" to each seam for seam allowance and then adding enough room at the top to make a casing. I then placed my pattern onto the fabric, with the outsides of the leg on the fold of the fabric, cut, and sewed the two pieces together. I did add contrasting fabric for the hem and casing ... just for fun. Ok, that description of how to make these stinks ... if you think that's bad ask me to explain a math problem to you - you'll be far more confused than when you started ... but if you google you'll find many great descriptions
of how to trace pants and make your own.
The onesie I had nothing to do with, and while it may not be a perfect match I, for some strange reason, think it's wonderful. :)
Using fabric I already had (and only a small amount of it) and tracing a pattern instead of buying one this project was, pretty much, free. The pants took about 20 or so minutes to make and will last him quite a while. In the future I'll make them wider and then, as was suggested before, let them be shorts as he gets bigger.