I know it has been a while since this post was started, but I have only just found this site.
Before I came across this site, I found another which had a tutorial for making denim dungaree's from an old pair of jeans.
It may help you, if you haven't made anything yet.
http://www.cutoutandkeep.net/projects/toddler_dungareesI hope it is of use to you or others looking for the same.
Ruth
EDIT:
Found another one:
http://www.ikatbag.com/2011/02/boy-shortalls-on-made-by-rae.htmlHere is the above but for girls:
http://www.ikatbag.com/2011/03/overalls-adaptation-for-girls.html