At Whits End

No actual advice from me, just that you may just want to skip the jeans.
My daughter is skinny, so finding a fitting pair was never a problem, but I have NEVER found a pair of jeans for her as a baby/toddler that was actually comfortable for her - she always hated them, even when they seemed flexible and she had lots of room in them.
At that age they move so much in all directions, I find that jeans just can't keep up with all of their crawling and climbing and so we eventually just stuck with the legging type play pants. If you are concerned that they may not be warm enough just put a pair of tights under them in the winter.

What about jeggings? They are way more comfortable anyhow. My daughter had the same problem, so we just did leggings because jeggings weren't around. Had we had that option, that is what we would have done!

One thing I just found and love are jeggings for my DD at Target $8 each. They seem so much more comfortable than jeans and they have give in every area. Good luck!

I just kept my daughter in leggings and stretchy cotton pants. Jeans were not comfortable for her and she didn't like them. She also was not shaped like most jeans were.

Hope this helps :)
http://www.llbean.com/llb/shop/69993?feat=6142-CL2

My son was/is a chunk. The ONLY pants that fit him last year were Kmart brand jeans. Seriously the ONLY ones that would.

Have you tried carters? They always seem big on the thighs. My daughters are 22mnths now and they still fit in 18mnths and still big on them...